WASHINGTON — The American military strike against Syria threatened Russian-American relations on Friday as the Kremlin denounced President Trump’s use of force and the Russian military indicated it would suspend an agreement to share information about air operations over the country that was devised to avoid accidental conflict.
Mr. Trump, who has made it a central goal of his presidency to improve strained ties with Moscow even amid criticism of Russian meddling in last year’s election, found that goal now at risk as both sides traded harsh words in a diplomatic confrontation reminiscent of the darkest moments of the last few years.
President Vladimir V. Putin’s office called the missile strike on Syria a “significant blow” to the Russian-American relationship, while Trump administration officials suggested Russia bore some responsibility for the chemical weapons attack on Syrian civilians that precipitated the American response.
The missile strike demonstrated the potential dangers of Russian and American forces’ operating in proximity, and American military planners acted to avert a direct conflict. Fewer than 100 Russian troops deployed in support of the Syrian government of President Bashar al-Assad were believed to be stationed at the Syrian air base targeted by American forces. An American official said the Russians on the ground were given just 60 to 90 minutes of advance notice that the cruise missiles were coming and were not advised whether to take shelter or flee.
Although Russia did not deploy its air defense system in Syria against the American cruise missiles, it flexed its military muscles after the attack. Russia said it would bolster Syria’s air defenses, while the Russian news agency Tass reported that a frigate would enter the Mediterranean Sea on Friday and would visit the logistics base at the Syrian port of Tartus.
Whether Russia would actually suspend the communication system with the Americans used to avoid accidental air clashes or bombing of ground targets was unclear.
Although Russian officials said they would freeze the system in response to the missile strike, American military officials said on Friday that it had not been suspended — so far, at least — and in fact it had been used earlier in the day.
American officials faulted Russia for not enforcing a 2013 agreement it brokered with Syria to eliminate all of its chemical weapons.
“Clearly, Russia has failed in its responsibility to deliver on that commitment from 2013,” Secretary of State Rex W. Tillerson said on Thursday night. “So either Russia has been complicit or Russia has been simply incompetent in its ability to deliver on its end of that agreement.”
Russia denied that Syria had any such weapons or that Damascus was behind the attack in Idlib Province on Tuesday that left more than 80 people dead, an attack that Western officials have said was conducted with sarin, a lethal nerve agent. Moscow said the attack was a false pretext to launch an air assault against Mr. Assad’s government.
“The Syrian Army has no chemical weapons at its disposal,” said Dmitri S. Peskov, a spokesman for Mr. Putin, blaming the gas attack on “terrorists.” Russia called on the United Nations Security Council to convene an emergency meeting, and Mr. Peskov said Mr. Putin considered the missile strike a breach of international law.
Syria on Friday condemned the American strike as “a disgraceful act,” news agencies reported. A statement from Mr. Assad’s office said the cruise missile strike was the result of “a false propaganda campaign.” Syria has denied that it possesses chemical weapons.
The cruise missiles struck Al Shayrat airfield at 3:40 a.m. local time (8:40 p.m. in Washington), targeting the same base that American officials said conducted the chemical weapons attack. The missiles were aimed at Syrian aircraft, hardened aircraft shelters, radars, air defense systems, ammunition bunkers and fuel storage sites. American military planners avoided targeting sites that they suspected of holding chemical agents, officials said.
Syrian officials and news outlets reported that six soldiers and nine civilians were killed. Talal Barazi, the governor of Homs Province, said the civilians died from shrapnel.
A spokesman for the Russian military, Maj. Gen. Igor Konashenkov, issued a statement calling the military effectiveness of the American airstrikes “extremely low,” asserting that just 23 of the 59 missiles hit their targets.
The American missiles destroyed a warehouse of material and technical property, a training building, a canteen, six MIG-23 aircraft in repair hangars and a radar station, according to the Russian military. A Russian television reporter, Evgeny Poddubny, who was at the air base, said nine planes were destroyed.
The strike plan was put together at the United States Central Command in Tampa, Fla., over a 48-hour period. When Defense Secretary Jim Mattis met with Mr. Trump on Thursday in Florida, where the president was hosting China’s visiting president, the options had already been winnowed down to a Tomahawk cruise missile strike at Al Shayrat.
Two American destroyers, the Porter and the Ross, were already in position in the eastern Mediterranean. But there was a window during which the middle-of-the-night attack was deemed most likely to minimize civilian casualties, and the question for Mr. Trump was whether to go ahead or wait another day. Mr. Trump opted to go ahead.
The presence of Russian military personnel near the airfield complicated the decision. Given their presence, American officials said they must have known about or turned a blind eye to the Syrian chemical weapons. American officials used the communications system previously set up to avoid conflict to notify the Russian forces on the ground. The conversation was described as lengthy, with the Russians doing much of the talking.
The chemical assault on Tuesday struck the town of Khan Sheikhoun, killing scores and sickening hundreds more. Turkey said on Thursday that sarin, a banned nerve agent, had been used in the attack, one of the worst atrocities of the Syrian war. American officials said that intelligence agencies had monitored the attack, mapping the radar tracks showing Syrian warplanes leaving and returning to the base.
The attack killed 84 and 546 others were injured, Tarik Jasarevic, a spokesman for the World Health Organization, told reporters in Geneva, citing health officials in Idlib Province.
Iran, Russia’s main ally in the region in buttressing Mr. Assad, condemned the American attack as “dangerous, destructive and a violation of international law.” Bahram Ghasemi, a spokesman for the Iranian Foreign Ministry, said in a statement that the missile strikes would lead to “the strengthening of failing terrorists” and complicate the situation in the region.
The British defense secretary, Michael Fallon, expressed support for the American strikes. “One of the purposes of this very limited and appropriate action was to deter the regime from using gas in this appalling way,” he told the BBC.
In a joint statement, Chancellor Angela Merkel of Germany and President François Hollande of France said that Mr. Assad, the Syrian president, “bears sole responsibility.”
A spokesman for President Recep Tayyip Erdogan of Turkey, Ibrahim Kalin, said the American strikes had been a positive response to “war crimes” in Syria, where the six-year civil war has led to nearly 400,000 deaths and created a refugee crisis as millions sought to flee. Mr. Kalin also repeated Turkey’s call to immediately set up and enforce a no-fly zone to create safe areas in Syria for those fleeing the violence.
The American strikes were also praised by Israel and by Saudi Arabia, two crucial allies of the United States in the Middle East. In a statement carried by the state news agency SPA, a Saudi official called the strikes a “courageous decision” by Mr. Trump. Prime Minister Benjamin Netanyahu of Israel said he hoped the action would “resonate not only in Damascus, but in Tehran, Pyongyang and elsewhere.”
Mr. Peskov, the Kremlin spokesman, gave no clear indication of how Russia might respond, and analysts suggested that the Kremlin had few options.
Russia could treat the strikes as a one-time event, limiting its response to criticizing the American aggression and conceding a revitalized American influence in the region. American officials have indicated that no other strikes were planned for the immediate future.
Russia could also try to confront the Americans more directly, but that would have unpredictable consequences. “There will be many screams on the Russian television with people condemning the strikes, but everybody understands that this is just a symbolic act meant for Trump to look different from Obama,” Vladimir Frolov, a foreign affairs analyst, said in an interview. “There won’t be any tangible reaction; this was a one-off strike.”
Others suggested that the lack of a Russian military reaction in Syria pointed to a realistic approach.
“Its initial response was to huff and puff and call it unprovoked aggression, of course; it could do nothing less,” Mark Galeotti, an expert on the Russian military, wrote in an online commentary. He noted that Russia’s state-of-the-art air defense system, which had been deployed to Syria with great fanfare, was apparently not used against the American attack.
“Moscow might not like Washington’s response, but nor was it willing to stand in the way of it,” he said. “That is a heartening sign of realism.”
Moscow might wait to formulate a response until Tuesday, when Mr. Tillerson, the former chief executive of Exxon Mobil and an old friend of the Kremlin, is set to make his first visit to Russia as secretary of state.
Mr. Peskov said that the American attack would do nothing to advance the fight against international terrorism, which he called a priority for Mr. Putin and which he noted had also been a main pledge of the Trump campaign.
“Most important, from Putin’s point of view, this move doesn’t bring us closer to the end goal in a fight against international terrorism,” Mr. Peskov said. “On the contrary, this creates a serious obstacle for the building of an international coalition to fight it and to effectively resist this universal evil.”
Mr. Putin dispatched the Russian Army to Syria, which has long been Russia’s main ally in the Middle East, in September 2015 with the stated goal of fighting terrorism, although the main purpose of the deployment was to shore up Mr. Assad, whose rule was faltering.
Other officials were quick to compare the cruise missile attack to other American interventions, in the Middle East and elsewhere, that ended poorly.
The Russian foreign minister, Sergey V. Lavrov, cited the American invasion of Iraq. “This is reminiscent of the 2003 situation, when the United States and the United Kingdom, along with their allies, invaded Iraq without the U.N. Security Council’s consent,” Mr. Lavrov said at a news conference on Friday after a meeting in Tashkent, Uzbekistan, between foreign ministers of former Soviet states.
The question of whether the United States invaded Iraq without the approval of the Security Council has long been a matter of debate. Washington has asserted that previous resolutions gave it the authority to take action, but critics have argued that it needed explicit United Nations approval.
Russia has repeatedly defended Syria against the accusation that Damascus has used chemical weapons. In this case, Moscow said the strike on Tuesday had actually hit a chemical weapons warehouse controlled by insurgents, a version of events that has been widely dismissed by the West.
General Konashenkov also repeated the Russian assertion that all chemical weapons had been removed from Syrian government stockpiles, and he called on the United States to present evidence that Damascus had used them.
Mr. Peskov asserted that the Organization for the Prohibition of Chemical Weapons had declared Syria to be free of chemical weapons, although it did not quite do that.
In an initial statement after the attack on Tuesday, the organization said it was seriously concerned about the allegations and wanted to gather more information before coming to a judgment.
“The O.P.C.W. strongly condemns the use of chemical weapons by anyone, anywhere and under any circumstances,” the group said.
Mr. Peskov said that the United States had launched its attack to distract attention from the high number of civilian casualties caused by a recent American airstrike in Mosul, Iraq.
As American and Russian governments quarreled over the strike, United Nations officials said on Friday that heavy fighting in other parts of Syria had recently killed hundreds more civilians. Bombing of Idlib and Raqqa provinces in recent weeks, including by the United States-led coalition, was the most intensive recorded in Syria’s more than six-year-old conflict, said Ravina Shamdasani, a spokeswoman for the United Nations’s human rights office.
More than 130 civilians were killed and 170 injured in the same month in Raqqa, the nerve center of the Islamic State in Syria, the vast majority in coalition airstrikes, Ms. Shamdasani said. Syrian government airstrikes conducted over two days in early April on the Eastern Ghouta suburb of Damascus had killed at least 42 civilians, she added.
Jan Egeland, the United Nations special adviser for Syria, said on Thursday that humanitarian agencies had reached only one of the towns besieged by government forces in the past month and were making little progress reaching the nearly 5 million Syrians who are trapped in areas where access is difficult because of fighting.
An estimated 400,000 civilians in Eastern Ghouta were running out of food and medicine. “This is the story of armed men supported by powerful men outside that sabotage, block, deny humanitarian access while the civilian population is attacked, gassed and bombed,” he said.