"Our units continue advancing in the direction of Vugledar," said Denis Pushilin, the Kremlin-appointed leader of the Donetsk region.

"Now we can say that units have established positions in the eastern part of Vugledar, and work is also being carried out in the vicinity," he said on Russian television.

A Ukrainian military spokesman in charge of the area said that Russia's attacks were unsuccessful.

"The enemy was hit by... firearms and artillery. The enemy had no success and retreated," Yevgen Yerin told AFP.

"We did not lose our positions," he added.

According to Pushilin, Ukraine's forces have "had time to gain a foothold" in Vugledar which has a "large number of industrial facilities and high-rise buildings" that facilitate defensive operations.

Russia's defence ministry said its troops had taken up "more advantageous positions" in Vugledar and inflicted losses on Ukrainian forces.

Kyiv said last week that "fierce" fighting was underway for control of Vugledar, a town that had a population of around 15,000 before the war.

It is about 150 kilometres (93 miles) south of Bakhmut, where months of fighting have led to heavy losses on both sides.

Pushilin said "fierce battles" were ongoing near Bakhmut but that it was "too early" to talk about the encirclement of the city.

"Fighting is ongoing, we are holding the defence and inflicting losses," Sergiy Cherevaty, another Ukrainian military spokesman, told AFP.

Kremlin-backed separatists have controlled parts of the industrial region of Donetsk, including its largest city, since 2014.

Moscow now seeks to capture the entire region after declaring it part of Russia last year.

Ukrainian President Volodymyr Zelensky said Sunday the situation on the front was "very tough", adding that Bakhmut, Vugledar and other areas in the region of Donetsk are "under constant Russian attacks".

"The enemy doesn't count its people and, despite numerous casualties, maintains a high intensity of attacks," Zelensky said.