The Ukrainian military said on Saturday that it had pushed Russian forces back by about 2 kilometres (1.2 miles) on part of the Sumy front in northern Ukraine.

Russia is racing to seize as much Ukrainian territory as possible ahead of peace talks with Donald Trump on Friday.

Ukrainian President Volodymyr Zelensky said Russia refusing to accept a ceasefire was complicating efforts to end Moscow's more than three-year-long conflict against his country.

"What has been building up for the Ukrainians is fundamentally a manpower issue," a former senior Pentagon adviser told Newsweek.

Granta Autonomy makes drones that are used by Ukraine, and its CEO said testing in Ukraine is so important that he visits the battlefield himself.

Moscow’s forces have rapidly gained ground in eastern Ukraine ahead of talks with Donald Trump when Vladimir Putin is expected to demand territory as part of a ceasefire deal.

Ukrainian troops have stabilised the battlefield in an area of eastern Ukraine where Russian forces had made a sudden push this week to pierce Ukrainian defences, the regional governor said on Thursday.

In recent days, Russia’s troops broke through a segment of Ukraine’s defensive line near the city of Pokrovsk, a Ukrainian stronghold in the Donetsk region. Russian forces have partly surrounded the city and are likely to tighten the noose around Pokrovsk to force Ukrainian troops to withdraw, a tactic they have used to capture other cities.