The chief of Russia's general staff told President Vladimir Putin on Thursday that Russian forces had taken control of the northeastern Ukrainian city of Kupiansk, but Ukraine's military denied the city had changed hands.

Ukraine also dismissed Russian statements that its forces had taken over large parts of two other towns – Pokrovsk, a logistics hub it has been pressing to capture for months, and Vovchansk, near the Russian border.

Putin had visited the command post of the Russian forces "West" grouping, where he met with chief of staff Valery Gerasimov, and top military brass, the Kremlin said earlier.

Putin had been briefed on the situation in two key cities in Ukraine's east – Kostiantynivka and Kramatorsk – as well as around Kupiansk in Kharkiv region, the Kremlin said.

"Units of the 'West' grouping have liberated the city of Kupiansk and are continuing to destroy Ukrainian armed forces units surrounded on the left bank of the Oskol River," Gerasimov told Putin in a video posted on the Kremlin site.

Gerasimov, seated among top officers opposite Putin, who was also in military uniform, told the president that Russian forces had taken control of 70 percent of Pokrovsk. He said more than 80 percent of Vovchansk was also under Russian control.

The heaviest fighting along the 1,200-km front line was near Pokrovsk, he said, with Ukrainian forces offering "stiff resistance".

It was not clear from the video exactly where the meeting with Putin had taken place.

A late-evening statement by the Ukrainian military said: "The General Staff of Ukraine's armed forces hereby announces that Kupiansk is under the control of Ukraine's defence forces."

"Also untrue are statements suggesting that 80 percent of Vovchansk in Kharkiv region has been captured and 70 percent of the city of Pokrovsk," it added.

The general staff reported heavy fighting in the Pokrovsk sector, with Russian forces launching 56 attacks.

Russian forces have been engaged in a slow westward advance through Donetsk region as part of their campaign to capture all of the Donbas – made up of the Donetsk and Luhansk regions.

Russian forces have also made recent gains further south in Zaporizhzhia region. They currently hold about 19 percent of Ukraine's territory. (Reuters)