Has Blackwater been deployed to Ukraine? Notorious U.S. mercenaries 'seen on the streets of flashpoint city' as Russia claims 300 hired guns have arrived in country

Unidentified armed men seen on the streets of Donetsk in east Ukraine

Russian diplomat claims 300 mercenaries had arrived in Kiev this week

Mercenaries in the region could give Putin pretext for military action

Donetsk has been the scene of big pro-Russian demonstrations this week

Speculation was growing last night that American mercenaries had been deployed to Donetsk after videos emerged of unidentified armed men in the streets of the eastern Ukrainian city.

At least two videos published on YouTube earlier this week show burly, heavily armed soldiers with no insignia in the city, which has been gripped by pro-Moscow protests.

In one of the videos onlookers can be heard shouting 'Blackwater! Blackwater!' as the armed men, who wear no insignia, jog through the streets.

Both the videos which purport to show 'Blackwater' mercenaries in Donetsk were uploaded last Monday, with their descriptions written in Russian.

The context of the videos is not clear, but it appears that the armed men had turned up at a street protest against the new regime. They wander around brandishing their weapons before suddenly fleeing the scene as passers-by shout 'Blackwater! Blackwater!'