The accusation quickly dented any sense of cautious optimism from Tuesday's late-night talks between presidents Vladimir Putin and Petro Poroshenko on resolving the five-month conflict.
Ukrainian military spokesman Andriy Lysenko said a group of Russian soldiers had crossed the border in armoured infantry carriers and a truck and entered the town of Amvrosiyivka, not far from where Ukraine detained 10 Russian soldiers on Monday.
Mr Lysenko said fighting in the towns of Horlivka and Ilovaysk to the north and east had killed about 200 pro-Russian separatists and destroyed tanks and missile systems. He said 13 Ukrainian service personnel had been killed and 36.
No comment was immediately available from the Russian defence ministry on the latest alleged incursion.
However, the Russian paratroopers captured on Monday said at a news conference in Kiev yesterday they had embarked on what they believed was a routine training patrol and had not realised they were on Ukrainian territory until their detention.