Russian President Vladimir Putin expressed his condolences to the families of the people killed in an air crash over the Black Sea on Sunday (December 25) and declared Monday a national day of mourning.

"First of all I would like to express the most sincere condolences to the families of our citizens killed this morning in an air crash over the Black Sea.

"The government was asked to form a commission which will be headed by the transport minister.

"A thorough investigation of the causes of the crash will be carried out and everything will be done to support the families of those killed.

"A national day of mourning will be held in Russia tomorrow," Putin said in a televised comments in St.Petersburg, standing next to his Kazakh counterpart Nursultan Nazarbayev.

The two presidents met in Russia's second largest city the day before a Monday meeting of the Collective Security Treaty Organization.

A Russian military plane carrying 92 people, including dozens of Red Army Choir singers, dancers and orchestra members, crashed into the Black Sea on its way to Syria on Sunday, killing everyone on board, Russian authorities said.

The Russian Defense Ministry said one of its TU-154 Tupolev planes had disappeared from radar screens at 0525 local time (0225 GMT) two minutes after taking off from Sochi in southern Russia, where it had stopped to refuel from Moscow, on its way to Syria.