"Air, rocket and artillery forces are carrying out massive strikes on units of the Ukrainian armed forces in all operational directions," the Russian defence ministry said in its daily briefing on the conflict.

Russia has pulled back its forces from swathes of northeast Ukraine, particularly in the Kharkiv region, after Ukrainian troops launched a lightning counter-offensive to wrest back territory held by Moscow's forces.

The defence ministry said in a statement it had launched "high-precision" strikes on Ukrainian positions around Sloviansk and Konstantinovka in the eastern Donetsk region.

Moscow's forces in the region, which has been partially controlled by Moscow-backed separatists since 2014, have reported fierce battles with Ukrainian forces over recent days.

The Kremlin meanwhile accused Kyiv's army of abusing civilians in territory it had recaptured.

President Vladimir Putin's spokesman said that in the Kharkiv region, reports were emerging of "outrageous" treatment of civilians.

"There are a lot of punitive measures... people are being tortured, people are being mistreated and so on," Dmitry Peskov told journalists.