"Each battalion task force consisted of about 300-350 people, and there were two of them," Lysenko said.

"The battalions crossed the Ukrainian-Russian border in Luhansk region, [at a part] that wasn’t controlled by the Ukrainian armed forces. Where these groups went after that is still unknown," he said.

As UNIAN reported earlier, on Monday the Information and Analytical Centre of the National Security and Defense Council reported that two battalions of Russian troops had crossed the border from Russia into Ukraine.

"According to the latest information of the National Security and Defense Council, today two battalion task forces of the Russian Federation were spotted crossing the Ukrainian - Russian border," the report said.