49 Ukrainian troops have reportedly been killed, after pro-Russian rebels shot down a military transport plane in the eastern Ukrainian city of Luhansk.

The Defence Ministry says it was targeted as it tried to land.

Ukrainian authorities have expressed their condolences to the parents and relatives of those killed.

Spokesman Vladyslav Seleznyov says the death toll would be the biggest suffered by government forces in a single incident since Kiev started a military operation to try to defeat the insurgency in east Ukraine.

It comes after Russia was accused by the US State Department of sending tanks and heavy weaponry to Ukraine in support of separatists in the country's east.

Several tanks and rocket launchers were moved into Ukraine from an arms depot inside Russia, the department said.

Moscow has denied the allegation.