A huge search operation is continuing "round the clock" in Russia, after a Russian military plane with 92 people on board crashed into the Black Sea.

More than 3,000 people, including 109 divers, as well as ships, planes, helicopters and submersibles are involved in the operation near Sochi.

The Tu-154 plane - carrying soldiers, members of a famed army music ensemble and reporters - was heading for Syria.

All those on board the aircraft are feared dead after Sunday's crash.

Monday has been declared a day of national mourning across Russia.

First bodies found

"As darkness fell, the operation in the rash area is continuing non-stop," defence ministry spokesman Maj Gen Igor Konashenkov said at a briefing late on Sunday.

He said that powerful spotlights were being used overnight as the search teams were looking for plane debris.

Officials earlier said they were were focusing on the area of 10.5 sq km (four square miles) just off the coast.

The defence ministry said in a statement: "Fragments of the Tu-154 plane of the Russian defense Ministry were found 1.5km (one mile) from the Black Sea coast of the city of Sochi at a depth of 50m to 70m (165-230ft)."

Earlier on Saturday, 11 bodies had been recovered. Asked by reporters if it could have been a terrorist attack, Russian Transport Minister Maksim Sokolov said investigators were looking into an "entire spectrum'' of possible causes of the crash.

But he stressed that it was too early to make any conclusions.

The plane disappeared from radar two minutes after taking off from Sochi's Adler airport at 05:25 (02:25 GMT), heading for Latakia in Syria, the defence ministry said.

The flight had originated in Moscow and landed in Sochi for refuelling.

It was carrying 64 members of the famed Alexandrov military music ensemble, who were to perform for Russian troops in Syria.

What is the Alexandrov Ensemble?

Alexandrov Ensemble is the official choir of the Russian armed forces

It was founded in 1928 during the Soviet era

The group also includes an orchestra and dancers

It takes its name from its first director, Alexander Vasilyevich Alexandrov, who wrote the music to the national anthem of the Soviet Union

Holds the right to use the term Red Army Choir, although the interior ministry's MVD Ensemble also uses it

An audio recording played on Russian media and said to be of the final conversation between air traffic controllers and the plane reveals no sign of any difficulties being faced by the crew.

Voices remain calm until the plane disappears and the controllers try in vain to re-establish contact.

Russia officials said flying conditions were favourable.

The plane came into service in 1983.

Maj Gen Konashenkov said the aircraft was last serviced in September and had undergone more substantial repairs in December 2014. It had an "experienced" pilot, he said.

The defence ministry has published a passenger list (in Russian), showing that Alexandrov Ensemble director Valery Khalilov was also on board.

There were nine journalists, eight soldiers, two civil servants and eight crew members.

Among the victims was Elizaveta Glinka, known as Dr Liza, the executive director of the Fair Aid charity and the inaugural winner of Russia's state prize for achievements in human rights.

The Alexandrov Ensemble was scheduled to perform a New Year's concert at Russia's Hmeimim air base near Latakia.

Russia has been carrying out air strikes in support of Syrian government forces who are battling rebels opposed to Syrian President Bashar al-Assad.

The plane was travelling from Tel Aviv in Israel to Novosibirsk in Russia, and most of the passengers were Israeli.

The Ukrainian military initially denied involvement but officials later admitted the plane could have been hit accidentally during a training exercise.# Source:BBC.com