The shooting is said to have taken place in the Belgorod region in southwestern Russia, which borders Ukraine.

Moscow's defence ministry said that the two men from an unnamed former Soviet nation opened fire on other soldiers during target practice, before being killed by return fire.

The ministry called the incident a terrorist attack.

The shooting comes after President Vladimir Putin ordered a hasty mobilisation to beef up the Russian forces in Ukraine.

Earlier, the defence ministry in Belarus released images of Russian troops arriving in the country as part of a "regional grouping".

Pictures showed a band playing and female troops presenting food to Russian soldiers.

Meanwhile, the UK Ministry of Defence said that many of the reserve troops being called up by Russia are probably having to buy their own body armour.

Some 300,000 reservists are being called up, according to Russia, as it seeks to halt a wave of successful Ukrainian counter-attacks. However, the MoD said their equipment "is almost certainly lower than the already poor provision of previously deployed troops".

The substandard kit comes on top of expert assessments that many of the reservists will be poorly prepared and trained for war on the frontline.

President Putin said on Friday that the call-up would be over in two weeks.

Sky News