Ukrainian troops are involved in very tough fighting near the strategically important eastern town of Bakhmut, which Russia is trying to take, President Volodymyr Zelenskiy said in a video address on Saturday.

Although Ukrainian troops have recaptured thousands of square kilometres of land in recent offensives in the east and south, officials say progress is likely to slow once Kyiv's forces meet more determined resistance.

Russian forces have repeatedly tried to seize Bakhmut, which sits on a main road leading to the cities of Sloviansk and Kramatorsk. Both are situated in the industrial Donbas region, which Moscow has yet to fully capture.

"We are holding our positions in the Donbas, in particular in the Bakhmut direction, where it is very, very difficult now, very tough fighting," said Zelenskiy (above).

Zelenskiy reiterated a call for western allies to provide greater amounts of anti-aircraft systems.

Russian forces are continuing to fire missiles at Ukrainian cities, and Kyiv accuses them of using Iranian suicide drones.

An official in the southern town of Zaporizhzhia said a Russian missile had hit a building late on Saturday.

Separately, officials said the death toll from a Russian rocket attack against Zaporizhzhia on Thursday had risen to 18.

- Reuters