Russian President Vladimir Putin on Thursday accused Ukraine of trying to attack the Kursk nuclear power station, some 50 kilometres (30 miles) from where Kyiv's forces are mounting a major cross-border offensive.

Moscow meanwhile said it was gaining ground in east Ukraine, while Russian officials accused Kyiv's forces of attacking and sinking a cargo ferry moored at a port near the annexed peninsula of Crimea.

"The enemy tried to strike the nuclear power plant at night. The International Atomic Energy Agency (IAEA) has been informed," Putin said during a televised government meeting on Thursday.

Putin did not present any evidence for his claims or provide further details on the alleged attack.

The claim came hours after the IAEA said its chief would visit the facility next week, with Russia having repeatedly sounded the alarm over a possible hit since Ukrainian troops and tanks stormed into its western Kursk region on August 6.

That offensive is now into its third week, with Kyiv laying claim to dozens of Russian border settlements and Russia scrambling to fight off the most serious attack by a foreign army on its territory since World War II.

There were no previous reports of the attempted strike on the facility in Russian media.

Kursk regional governor Alexei Smirnov told Putin the facility was working as usual.

There was no immediate reaction from officials in Kyiv to Putin's claim.