Moscow's troops seized the facility -- Europe's largest nuclear power station -- in the first days of its invasion of Ukraine, and both sides have repeatedly accused the other of risking a potentially devastating nuclear disaster by attacking the site.

Staff from the UN nuclear watchdog have been based there since September 2022 to monitor nuclear safety.

Fighting meant the IAEA staff could not be swapped out as part of a planned rotation on Wednesday -- the second such delay in a week -- both Kyiv and Moscow said, trading blame for the incident.

Ukrainian foreign ministry spokesman Georgiy Tykhy said in a statement: "Russia has once again deliberately disrupted the rotation of IAEA experts at the Zaporizhzhia plant."

Inspectors spend around five weeks at the plant in stints before being swapped out in a complex procedure that involves travelling across the front line under supervision from the Russian and Ukrainian militaries.

Tykhy accused Russia's army of opening fire near where the planned rotation was taking place, saying Moscow's goal was to force the IAEA team to travel through Russian-controlled territory and "violate Ukraine's sovereignty and territorial integrity."

Russia's foreign ministry spokeswoman Maria Zakharova said the Ukrainian army blocked the IAEA team from travelling to an agreed meeting point and were attacking the area with drones -- at which point the Russian military withdrew its support team and returned to the station.

"On their return, the convoy carrying Russian military personnel and IAEA experts... came under attack by drone and mortar strikes," Zakharova said in a statement.

The IAEA staff members were supposed to leave the station on February 5 in a rotation that was also delayed.

IAEA head Rafael Grossi was in both Ukraine and Russia last week, where he discussed the issue of rotations with officials from both countries.

In a statement, Grossi expressed his "deep regret" over the cancellation of the "carefully prepared and agreed rotation" due to excessive danger, calling the situation "completely unacceptable".

"As a result of these extremely concerning events, I am in active consultation with both sides to guarantee the safety of our teams," he said.