SOCHI, Russia — A Russian aircraft bound for Syria carrying a famed military band to entertain Russia’s forces there crashed into the Black Sea moments after takeoff Sunday, and the authorities said all 92 people aboard were believed dead.
The cause of the crash is under investigation, although initial Russian news media reports indicated it was a technical failure rather than terrorism.
The Russian military has had only minor casualties throughout its deployment in Syria, but the country has experienced a series of setbacks in recent days.
That came not long after forces from the Islamic State recaptured the storied Syrian city of Palmyra, forcing the Russian garrison that had been stationed there since helping to take the city last spring to flee.
The military plane, a Russian-made Tupolev Tu-154, disappeared from radar two minutes after taking off from the resort town of Sochi. Russia’s official weather forecast agency said that conditions near the airport were “normal, easy,” the Interfax news agency reported. The airplane was technically fit, the Defense Ministry said.
Wreckage of the plane, which was carrying 84 passengers and eight crew members, was found in the sea, most of it about one mile from shore, the Russian Defense Ministry said. No survivors have been found at the crash site, Russian officials said.
Passengers on the flight, which originated in Moscow and stopped in Sochi to refuel, included 64 members of the Alexandrov Ensemble, the Russian military choir, who were traveling to Russia’s Khmeimim Air Base in Syria. The band planned to serenade Russian personnel in Syria on New Year’s Eve.
President Vladimir V. Putin deployed Russian armed forces in Syria in September 2015, ostensibly to fight terrorism but primarily to prop up President Bashar al-Assad, the leader of the lone remaining Russian ally in the region, whose forces have been fighting an insurgency for nearly six years.
Russian forces have been instrumental in helping the Damascus government regain the initiative, with the final rebels expelled from the besieged city of Aleppo on Thursday.
Three journalists from Channel One, Russia’s main television station, were on the plane, as were journalists from the Zvezda and NTV television networks, news reports said.
Yelizaveta P. Glinka, a prominent Russian philanthropist and a member of the presidential council on human rights and civil society, was also on the list of people on board. Mr. Putin recently honored Mrs. Glinka with a state award for her human rights and charity work. Valery V. Khalilov, the ensemble’s artistic director, was also on the plane, according to the list of passengers.
Mr. Putin expressed his condolences to relatives of the victims, and he declared Monday a national day of mourning. (Christmas is not celebrated as an official holiday in Russia on Dec. 25, because the Russian Orthodox Church observes it on Jan. 7.)
“First of all, I would like to express my sincere condolences to the families of our citizens, who died today, as a result of an aviation catastrophe over the Black Sea this morning,” Mr. Putin said in St. Petersburg, according to remarks published on the Kremlin’s website.
He also ordered Prime Minister Dmitri A. Medvedev to establish a state commission, headed by the transportation minister, Maxim Sokolov, to investigate the crash. The Defense Ministry said that 11 bodies had been recovered as search efforts continued, Russian news agencies reported.
A makeshift memorial was installed inside the Sochi airport, and people brought candles and flowers. Relatives of the victims were whisked away by the authorities to a specially designated zone, where they were treated by psychiatrists.
Mr. Sokolov told journalists inside the terminal building that the rescue effort would not stop at night.
“It is premature to say anything about the causes of this tragedy,” he told reporters.
More than 30 vessels were deployed in the recovery operation, Mr. Sokolov said, and the Defense Ministry said that more than 100 divers had been sent to the crash site.
Founded in the Soviet era, the Alexandrov Ensemble, which had performed in Syria earlier this year, is the official band of the Russian armed forces. It consists of an orchestra, a choir and a dance ensemble, and is one of the two Russian orchestras allowed to use the title “Red Army Choir.”
The ensemble was founded by Aleksandr V. Aleksandrov, a prominent Soviet composer and the author of the music of the Russian anthem, and his grandson Yevgeny told Meduza, a Russian news website, that “the best members of the ensemble died.”
“All the best soloists, the whole choir,” he said. “Everything will collapse now. The best ones are gone.”
Several independent news outlets in Russia reported that the Alexandrov Ensemble had planned to give a concert in Aleppo. In May, the Russian military had flown a symphony orchestra led by one of its best-known conductors, Valery Gergiev, to mark the reclaiming of Palmyra.
Until recently, the Tu-154, which was designed in the 1960s, was one of the most widely used civilian aircraft in Russian aviation. The plane that crashed on Sunday was made in 1983, underwent planned maintenance work in the fall, and was operated by an experienced pilot, the Defense Ministry said.
Russian airlines have mostly replaced outdated Soviet planes with new ones in recent years and have vastly improved the overall safety record. Many government agencies continue to fly the Tu-154 and other old Soviet aircraft, however.
The age and reputation of the Tu-154, as well as the fact that the aircraft had flown out of secure military airfields, meant that most senior officials speaking publicly ruled out the possibility that an attack had caused the crash. But there was speculation by a few aviation experts, echoed by some officials, that terrorism could not be ruled out given the suddenness with which the plane disappeared and the size of the debris field.
“For us the worst version is an act of terrorism, because if this is the case, this will mean that we have paid another bill for Aleppo,” Vadim Lukashevich, an aviation expert, told Dozhd, an independent television station.
In one of Russia’s most recent air disasters, the Islamic State claimed responsibility for planting a bomb onboard a Russian civilian Airbus that crashed in Egypt in October 2015, killing all 224 people on board in a flight from the Egyptian resort of Sharm el-Sheik to St. Petersburg.
Another Russian-made military plane crashed in eastern Siberia on Monday, seriously injuring 16 of the 39 people on board, and the aviation authorities recently grounded the country’s newest civilian airliner, the Sukhoi Superjet 100, because of concerns about metal fatigue.