KYIV - Ukraine's defence ministry said on Wednesday that Russia was attempting to increase the tempo of its offensive in the east of the country.

Defence Ministry spokesman Oleksandr Motuzyanyk gave few details but said Moscow had conducted nearly 50 air strikes on Tuesday alone.

He also said Russian artillery fire and air strikes were continuing periodically on the Azovstal steel works in Mariupol where the last Ukrainian defenders of the southern port city are holed up.

"Russia's military command is attempting to increase the tempo of its offensive operation in eastern Ukraine," Motuzyanyk told a briefing.

He said Russian strategic bombers had fired 18 rockets from airspace above the Caspian Sea at targets in Ukraine "with the aim of damaging our country's transport infrastructure."

The ministry's account of the military situation across Ukraine could not immediately be verified.

Russian forces have turned their heaviest firepower on Ukraine's east and south after failing to take Kyiv, the capital, in the opening weeks of the war.

When asked about the situation in the Azovstal steel works, Motuzyanyk said there had been Russian attempts to storm the plant. Mariupol Mayor Vadym Boichenko said separately that fighting at the plant continued on Wednesday.

Asked about the situation at the steel works, Kremlin spokesman Dmitry Peskov said: "The order was publicly given by the supreme commander (Russian President Vladimir Putin) to cancel the storming (of the plant). There is no storming."

"We see that there are escalations associated with the fact that fighters are taking up firing positions. These attempts are being suppressed very quickly, there is nothing else to say at the moment," he said.

(Reporting by Max Hunder, Additional reporting by Mark Trevelyan in London, Editing by Timothy Heritage)