The International Atomic Energy Agency (IAEA) said in a statement that the meeting of its board of governors would be held at 11 am (1000 GMT) on Wednesday at its Vienna headquarters.

Ukraine has four active nuclear power plants, as well as stores of nuclear waste such as the one at Chernobyl, and there have been fears over the possible consequences should they be damaged in the fighting.

Chernobyl was the site of the worst nuclear accident in history in 1986 and on Thursday the site fell to Russian troops.

Ukrainian authorities said that radiation levels had increased there following the Russian takeover but the IAEA said the levels remained low and did not "pose any danger to the public".

Also on Sunday the IAEA said it had been informed by Ukraine that "missiles hit the site of a radioactive waste disposal facility in Kiev overnight but there were no reports of damage to the building or any indications of a radioactive release".

That incident came a day after Ukrainian officials said an electrical transformer at a similar disposal facility near the northeastern city of Kharkiv had been damaged, but again there had been no reports of a radioactive release.

IAEA Director General Rafael Grossi said such incidents "highlight the very real risk that facilities with radioactive material will suffer damage during the conflict, with potentially severe consequences for human health and the environment".

"Once again, I urgently and strongly appeal to all parties to refrain from any military or other action that could threaten the safety and security of these facilities," he added.

Russian President Vladimir Putin on Sunday said he was putting Russia's nuclear forces on high alert because Western countries were taking "unfriendly" steps against his country in the wake of the invasion.

The IAEA's meeting on Wednesday will come days before a scheduled board of governors meeting and coincides with a crucial phase of efforts to fully restore the 2015 deal on Iran's nuclear programme.

Diplomats from Britain, China, France, Germany, Iran and Russia have been taking part in talks on reviving the accord in Vienna, with their success or failure widely expected to hinge on negotiations in the coming days.

The United States has been taking part in the talks indirectly.