An inspection team from the UN nuclear watchdog is on its way to Ukraine's embattled Zaporizhzhia nuclear power plant, the organisation's head said.

Rafael Grossi, director general of the International Atomic Energy Agency (IAEA) said the team was expected to arrive at the plant later this week.

"We must protect the safety and security of Ukraine's and Europe's biggest nuclear facility," he tweeted.

The nuclear plant has been occupied by invading Russian troops since March.

Fighting around the facility in Ukraine's south-east has led to mounting global concern over the safety and security of the site.

Ukraine and Russia have accused one another of shelling the area.

Ukrainian President Volodomyr Zelensky said Europe was "one step away" from a radiation disaster on Thursday when the plant was briefly disconnected from Ukraine's power grid and back-up generators kicked in to supply it with power.

He said fires had damaged the overhead power lines, cutting the plant off for the first time in its history.

Ukraine and Russia blamed each other for strikes that caused the damage. The BBC was not able to independently verify which side was responsible.

Russia's military took over the plant in early March, but it is still being operated by Ukrainian staff under difficult conditions.

The Kremlin had previously signalled that it would only allow international inspectors to visit the complex so the IAEA's visit will mark an important moment in being able to verify what is happening on the ground.

Ukraine had feared an IAEA mission to Zaporizhzhia would legitimise the Russian occupation of the nuclear plant, before finally backing a visit.

"Almost every day there is a new incident at or near the Zaporizhzhia nuclear power plant. We can't afford to lose any more time," the IAEA director general said.

Experts say shelling around the plant is not the main concern, given the plant has thick protection walls.

However, cutting the supply of electricity to it is fraught with danger. The loss of the power supply to the nuclear reactors and back-up generators would mean no power for the pumps cooling the hot reactor core and therefore leading to the fuel starting to melt.