Pro-Russian rebels in eastern Ukraine have been bolstered by 1,200 troops who "trained for four months in Russia", according to the separatists' leader.
A video recording of Alexander Zakharchenko speaking to delegates appears to confirm reports of Moscow's military support to the rebels, who have been fighting Ukrainian government troops since April.
Petro Poroshenko, Ukraine's president, claimed on Friday that his forces had destroyed part of a column of Russian military vehicles that crossed into Ukraine, with Nato accusing Moscow of launching an "incursion".
David Cameron, the Prime Minister, expressed his "grave concern" over reports of the breach, and Washington last night called for Moscow to halt its "extremely dangerous and provocative" actions.
In his speech, reportedly made on Friday at a "people's council" and posted on a rebel YouTube channel, Mr Zakharchenko said that on rebel-held territory, "the following reserves have been gathered:
150 armoured vehicles, of which about 30 are tanks and the rest are BMPs and BTRs [infantry fighting vehicles and armoured personnel carriers], 1,200 military personnel, who are there now, who underwent training for four months on the territory of the Russian Federation. They were brought into action at the most crucial moment." It was unclear whether Mr Zakharchenko, who is prime minister of the self-proclaimed Donetsk People's Republic, meant that the armoured vehicles also came from Russia.