Russian media say the two main theories under consideration by investigators are possible pilot error or a technical failure.
"The whole world is expressing its condolences to us. But it is impossible to forget this."
"We mourn," read an inscription listing the names of all 55 passengers and seven crew who died in the crash.
The plane's wing hit the ground on its second attempt to land and burst into flames
"Three foreigners were on the passenger list of the plane, but that information needs checking."