Moscow and Kyiv have accused each other of shelling the Zaporizhzhia plant, the biggest atomic power station in Europe, which has been under Russian control since March.

The tensions around the facility have sparked fears of another nuclear disaster in Europe like the one in Chernobyl in then Soviet Ukraine in 1986.

"Nobody could have predicted that Russian troops would be firing on nuclear reactors with tanks. It is incredible," Interior Minister Denys Monastyrsky said in the Ukrainian-held city of Zaporizhzhia, 50 kilometres (31 miles) from the plant.

After watching a nuclear accident drill on Wednesday, he said Ukraine should be prepared since "as long as the Zaporizhzhia nuclear plant is controlled by Russia, there are major risks".

Dozens of Ukrainian emergency workers wearing gas masks and hazmat suits took part in the drill in which they practised evacuating an injured person and washing down contaminated vehicles.

The head of Ukraine's state nuclear agency Energoatom, Petro Kotin, said around 500 Russian soldiers and 50 armoured vehicles were at the plant.

Russia has said it does not have any heavy weapons or troops there except for guard units.

Ukraine has accused Russia of firing on the plant in order to accuse Ukraine of doing it, while Russia has accused Kyiv of shelling the facility.

It is impossible to independently verify the claims.