MOSCOW, Jan 30 (Aljazeera) - Russia has begun its “big revenge” for Ukraine’s resistance to its invasion, Ukrainian President Volodymyr Zelenskyy has said, as Russian forces claimed a series of incremental gains in his country’s east.

Zelenskyy has been warning for weeks that Moscow aims to step up its assault on Ukraine after about two months of virtual stalemate along the front line that stretches across the south and east.

While there was no sign of a broader new offensive on Monday, the administrator of Russian-controlled parts of Ukraine’s eastern Donetsk province, Denis Pushilin, said Russian troops had secured a foothold in Vuhledar, a coal mining town whose ruins have been a Ukrainian bastion since the outset of the war.

Pushilin’s adviser, Yan Gagin, said fighters from Russian mercenary force Wagner had taken partial control of a supply road leading to Bakhmut, a city that has been the focus of a Russian offensive for months.

A day earlier, the head of Wagner said his fighters had secured Blahodatne, a village just north of Bakhmut.

Kyiv said it had repelled assaults on Blahodatne and Vuhledar. The Reuters news agency could not independently verify the situations there, but the locations of the reported fighting indicated clear, though gradual, Russian gains.

Zelenskyy said Russian attacks in the east were relentless despite heavy casualties on the Russian side, casting them as payback for Ukraine’s success in pushing Russian forces back from the capital, northeast and south earlier in the conflict.

“I think that Russia really wants its big revenge. I think they have [already] started it,” Zelenskyy said.

“Every day they either bring in more of their regular troops, or we see an increase in the number of Wagnerites,” he told reporters in Ukraine’s southern port city of Odesa.

Vuhledar sits south of Bakhmut, near where the eastern front line protects Russian-controlled rail lines supplying Moscow’s forces in southern Ukraine. Mykola Salamakha, a Ukrainian colonel and military analyst, told Ukrainian Radio NV that Moscow’s assault there was coming at a huge cost.

“The town is on an upland and an extremely strong defensive hub has been created there,” he said. “This is a repetition of the situation in Bakhmut — one wave of Russian troops after another crushed by the Ukrainian armed forces.”