Almost three years after invading, Russia's forces are accelerating their offensive, capturing more Ukrainian territory in November than in any month since March 2022, according to AFP analysis of data from the US Institute for the Study of War.

Kyiv said Russian forces had tried to cross the Oskil river, which has long been a de facto front line across the east of the war-scarred country.

The waterway winds its way from Russia's western border through the northeast of Ukraine, with Moscow and Kyiv's forces entrenched on either side of sections of its banks.

"As a result of the successful operation, the enemy was destroyed. The right bank of the Oskil river is under the control of the Defence Forces," the Ukrainian military said in a statement.

Ukrainian military bloggers had over recent days reported a Russian push over the river near the village of Novomlynsk in the northeastern Kharkiv region.

Moscow's forces have been advancing in the Kharkiv region, which borders Russia, and are closing in on the civilian hub of Kupiansk, which is divided by the Oskil river.

Kupiansk had a pre-war population of around 27,000 people and was occupied by Russian forces just days after the Kremlin launched its invasion, when the town's mayor ceded control.

Ukraine recaptured it in September 2022 as part of a lightning offensive that saw them regain large swathes of the Kharkiv region.

Russia's forces claimed separately on Tuesday to have advanced along the eastern and southern fronts.

The defence ministry said its troops had seized the villages of Novodarivka in the southern Zaporizhzhia region and Romanivka in the eastern Donetsk region.

It also claimed to have "improved its tactical position" in the northeastern Kharkiv region, including around Kupiansk, though did not comment on the alleged attempted river crossing.

Russia's troops have stepped up their advances on the frontline, combined with an escalation in aerial attacks on Ukrainian cities and energy facilities.

AFP analysis of ISW data showed that during November, Kremlin forces advanced over 725 square kilometres (280 square miles) of Ukrainian territory, mainly in the east near the city of Pokrovsk, compared with an advance of 610 square kilometres in October.