Russia claims its forces have captured the frontline town of Kurakhovo in eastern Ukraine's Donetsk region.
The city has borne the brunt of Russian advances in recent months and is a springboard to the key logistics hub of Pokrovsk.
Ukraine has not recognized the fall of Kurakhovo, which is 35 kilometers (21 miles) south of Pokrovsk.
Fierce fighting has also been taking place in the Kursk region of Russia in recent days Ukraine launched a counterattack on Sunday.
An image taken from social media and provided by the Reuters news agency appears to show a soldier holding a Russian flag in Kurakhove. The image has not been confirmed by the BBC.
Viktor Trehubov, a spokesman for the Ukrainian Khortytsa group, told Reuters that as of Monday morning, Ukrainian forces were still clashing with Russian troops in Kurakhovo.
Kurakhove is connected to Pokrovsk by roads that are part of the infrastructure for the movement of troops and supplies along the front line.
Taking Kurakhovo would allow the Russians to move north to attack Pokrovsk from a new direction, analyst Roman Pokhorili said.
The Russian Defense Ministry also said on Monday that the village of Dachenske, which is about 8 kilometers south of Pokrovsk, had been captured by its forces.
Kiev's forces have reportedly been short of manpower and have been losing ground in eastern Ukraine in recent months as Russian troops advance.