Ukraine on Sunday said the situation was "tense" on its eastern front, where the Russian army is doubling down on efforts to seize the strategic town of Chassiv Iar.

Ukrainian Defence Minister Rustem Umerov said he had visited troops on the frontier, where Ukrainian forces are outnumbered and running low on ammunition.

He said "the situation is tense," a day after Kyiv warned that the situation on its eastern front was significantly worsening.

If Moscow manages to capture Chassiv Iar, it would "create conditions for a deeper advance" towards the key Ukrainian transport hub of Kramatorsk, said Ukraine's commander-in-chief Oleksandr Syrsky.

Kramatorsk town is the major rail and logistics hub for the Ukrainian army, 30 kilometres from Chassiv Iar.

Russia has been trying to break through to the west of Bakhmut – a town conquered by the Russians in May 2023 after a bloody battle – according to Umerov.

In recent weeks, Moscow has claimed the capture of several small villages, notably near the industrial town of Avdiivka on Saturday.

It has also ramped up its aerial bombardments on Ukraine's infrastructure in recent weeks, with President Volodymyr Zelenskyy saying the Kremlin was aiming to drive people from its second city Kharkiv.

"Rhetoric does not protect the sky," Zelenskyy said on Sunday.

Zelenskyy said that only "tangible assistance" can stop missiles and drones, adding a plea for the release of US war aid for Ukraine that has long been blocked by Congress. (AFP)