Militants of the self-proclaimed Luhansk People's Republic walk in a trench at combat positions near the line of separation from the Ukrainian armed forces outside the settlement of Molodizhne (Molodezhnoye) in the Luhansk region, Ukraine February 17, 2022. (Photo:REUTERS)

For a second consecutive day, pro-Russian separatists who have been at war with Ukraine for years said they had come under mortar and artillery fire from Ukrainian forces, according to the Interfax news agency.

Kyiv and the rebels blamed each other for escalating tension after artillery and mortar attacks on Thursday, prompting fears that Russia, which has massed more than 100,000 troops near Ukraine's borders, could get involved.

The Kremlin said on Thursday it was "deeply concerned" with the flare-up in Ukraine and was watching the situation closely.

The United States said Russia was looking for a pretext for war.

Russia said it has no intention to invade Ukraine and accuses the West of hysteria over its military build-up, saying some of its troops have returned to bases.

Interfax news agency cited Russia's defence ministry as saying on Friday that several Russian mechanised infantry units had returned to their bases in the regions of Dagestan and Chechnya after completing drills in Crimea.