UN inspectors vowed to press on with a visit to a Russian-held nuclear power plant in southern Ukraine on Thursday despite an early shelling attack on the town next to the facility.

"We are aware of the current situation. There has been military activity.. several minutes ago," International Atomic Energy Agency chief Rafael Grossi told reporters just before leaving. "But we are not stopping."

His remarks came as the mayor of Energodar, the town next to the plant, said it had come under sustained attack early on Thursday.

Since dawn, Russian troops had "shelled Energodar with mortars and used automatic weapons and rockets," Mayor Dmytro Orlov said on Telegram, publishing pictures of damaged buildings with smoke spiralling above them.

But Moscow accused Kyiv of smuggling in up to 60 military "saboteurs" who reached the area near the plant just after dawn, saying Russian troops had taken "measures to annihilate the enemy".

"We know there is a grey area where the last line of Ukrainian defence ends and the first line of the Russian occupying forces begins where the risks are significant," Grossi before his 14-strong team left to cross the frontline into Russian-held territory.

"I believe we have to proceed with this. We have a very important mission to accomplish."

Grossi had on Wednesday said the IAEA would seek to establish a "permanent presence" at the plant to avoid a nuclear disaster at the facility which is located on the frontline of the fighting.

"My mission is... to prevent a nuclear accident and preserve the largest nuclear power plant in Europe," he said.

The area around the facility, which lies on the south side of the Dnipro River, has been hit by repeated shelling, stoking global concern.

Both sides have traded blame over attacks in the area.

- 'Explicit safety guarantees' -
Although Zaporizhzhia is normally about a two-hour drive from the plant, it was not immediately clear how the IAEA team would reach the site which would involve crossing the frontline to enter Russian-held areas.

The plant has been occupied by Russian troops since March and Ukraine has accused Russia of deploying hundreds of soldiers and storing ammunition there.

Kyiv has insisted the team access the plant via Ukrainian-held territory.

"Sadly, Russia is not stopping its provocations precisely in the direction the mission needs to travel to reach the plant," President Volodymyr Zelensky said late Tuesday after meeting Grossi.

In Moscow, the Russian defence ministry accused Kyiv of "continued provocations aimed at disrupting the work of the IAEA mission" saying it had shelled the area around the plant on Tuesday hitting a building containing "the solid radioactive waste processing complex".

- Counteroffensive in the south -
Meanwhile, intensive fighting raged across the nearby southern region of Kherson where Ukraine began a counteroffensive on Monday.

Most of the region and its provincial capital of the same name were seized by Russian forces at the start of the invasion six months ago.

With the war in the eastern Donbas region largely stalled, analysts have said for weeks that combat is likely to shift south to break the stalemate before winter comes.

As Ukraine presses its offensive, the White House said there would be an announcement in the coming days on additional military aid for Kyiv, on top of $13 billion already pledged by Washington.

Earlier on Wednesday, EU foreign ministers agreed to suspend a 2007 visa facilitation deal with Russia, which will make it more difficult and longer for Russian nationals to get visas.

Zelensky, who wants a total ban on EU tourist visas for Russians, said Wednesday that Russian society must pay the price for the war.

"I think it is humiliating for Europe when it is considered simply as one big boutique or restaurant," he said in his daily address to the nation. "Europe is a territory of values first of all, not primitive consumption."