Sochi — A pilot error or a technical fault is likely to be the cause of Sunday's plane crash over the Black Sea, the Russian transport minister said on Monday.All 84 passengers and eight crew members on the Russian military's Tu-154 plane are believed to have died when it crashed two minutes after taking off from Russia's Sochi. The passengers included dozens of singers in Russia's world-famous military choir.More than 3 000 rescue workers on 32 ships — including over 100 divers flown in from across Russia — were searching the crash site at sea and along the shore, the Defense Ministry said.Transport Minister Maxim Sokolov said in televised remarks on Monday morning that terrorism was not among the main theories, and that authorities are looking into a possible technical fault or a pilot error.Several experts noted factors that could suggest a terror attack, such as the crew's failure to report any malfunction and the fact that plane debris was scattered over a wide area.The plane, which originated from Moscow's military airport Chkalovsky and stopped in Sochi for refuelling, was taking the Defense Ministry's choir, the Alexandrov Ensemble, to perform at a New Year's concert at the Russian air base in Syria's coastal province of Latakia.Those on board also included nine Russian journalists and a Russian doctor famous for her work in war zones and helping homeless people.Sokolov said the government sees no need to heighten security measures at Russian airports.Emergency crews found fragments of the plane about 1.5 kilometres from shore, and by Monday morning, rescue teams had recovered 11 bodies. A plane with bodies from the crash has landed in Moscow where the remains will be identified, Sokolov said.Monday has been declared a nationwide day of mourning in Russia.The Tu-154 is a Soviet-built three-engine airliner designed in the late 1960s. More than 1 000 have been built, and they have been used extensively in Russia and worldwide. The plane that crashed Sunday was built in 1983, and underwent factory check-ups and maintenance in 2014, the Defense Ministry said.