A team of U.N. inspectors made its way toward Ukraine’s Zaporizhzhia nuclear power plant Wednesday on a perilous, long-sought mission to safeguard the site and prevent a catastrophe from the fighting raging around it.

Underscoring the danger, Kyiv and Moscow again accused each other of shelling the area around the complex overnight. Zaporizhzhia is the biggest nuclear plant in Europe.

Fighting in early March caused a brief fire at its training complex, and in recent days, the plant was temporarily knocked offline because of damage, heightening fears of a radiation leak or a reactor meltdown. Officials have begun distributing anti-radiation iodine tablets to nearby residents.

The complex has been occupied by Russian forces but run by Ukrainian engineers since the early days of the 6-month-old war. Ukraine alleges Russia is using the plant as a shield, storing weapons there and launching attacks from around it, while Moscow accuses Ukraine of recklessly firing on the place.

For months, as the fighting has played out, the head of the International Atomic Energy Agency has sought access to the plant for an unprecedented wartime mission, and world leaders have demanded that the U.N. watchdog be allowed to inspect it.

With the convoy of vans and U.N.-marked SUVs finally arriving in the afternoon in Zaporizhzhia city, still some 120 kilometers (70 miles) by road from the plant, IAEA chief and mission leader Rafael Grossi said the “real work” will start on Thursday. He underscored the challenges ahead.

“It’s a mission that seeks to prevent a nuclear accident and to preserve this important — the largest, the biggest — nuclear power plant in Europe,” he said.

He said an initial tour will take a few days, after which “we will have a pretty good idea of what’s going on.” Grossi said he had received “explicit guarantees” from Russia that the 14 experts would be able to do their work.

Grossi said he is hoping the IAEA will be able to establish a “continued presence” at the plant to safeguard it against an accident.

The world watched the mission’s progress with anxiety. European Union foreign policy chief Josep Borrell renewed a call to Russia to fully demilitarize the area around the plant.

“They are playing games. They are gambling with the nuclear security,” Borrell said. “We cannot play war games in the neighborhood of a site like this.”

While the inspectors were on their way, Russia-backed local authorities accused Ukrainian forces of repeatedly shelling the plant grounds and city where it is situated, Enerhodar. They said drone strikes hit the plant’s administrative building and training center.

Yevhen Yevtushenko, head of the administration in the Ukrainian-held city of Nikopol, across the Dnieper River from the plant, charged that the attacks were carried out by the Russians in a bid to make Ukraine look like the culprit.

Kyiv is seeking international assistance in taking back control of the area.

“We think that the mission should be a very important step to return (the plant) to Ukrainian government control by the end of the year,” Ukrainian Energy Minister German Galushchenko said.

In other developments:

— Russia’s Gazprom stopped the flow of natural gas through a major pipeline to Western Europe early Wednesday for what it said would be a three-day shutdown for routine maintenance. German authorities cast doubt on that explanation.

— EU countries agreed to make it more time-consuming and costly for Russian citizens to get visas to enter the 27-nation bloc. They failed to reach a consensus on an outright tourist ban in response to Russia’s invasion of Ukraine.

— Ukrainian officials said automatic weapons fire was heard on the streets of southern Kherson and claimed Russian soldiers were searching homes for anti-Russian partisans. A surge in fighting in the region this week stirred speculation early that Ukraine was beginning a counteroffensive to retake territory.

Russian forces heavily shelled military and civilian sites in over a dozen towns and villages in Kherson and the neighboring Zaporizhzhia region, according to Yaroslav Yanushevych, the Ukrainian governor of the Kherson region.

— Four people were killed and two wounded in Russian rocket attacks in the past day in the Donetsk region in the east, Ukrainian authorities said.