KYIV, Ukraine (AP) — A team from the U.N. nuclear agency has arrived at the site of Europe's largest nuclear plant to inspect security conditions that forced the shutdown of one reactor, Ukraine's nuclear energy operator said Thursday.

Enerhoatom said the team from the International Atomic Energy Agency had arrived at the Zaporizhzhia plant that has been in the thick of recent fighting between Ukrainian and Russian forces more than six months after Russian President Vladimir Putin ordered his troops to invade Ukraine.

The company said earlier Thursday that Russian mortar shelling led to the shutdown of one of its reactors by its emergency protection system.

Shelling also damaged a backup power supply line used for in-house needs, and one of the plant's reactors that wasn't operating was switched to diesel generators, the company said.

The company that oversees Ukraine's nuclear power plants said shelling by Russian troops forced the shutdown of one of the reactors at the Zaporizhzhia plant, underscoring the risks faced by a team of U.N. inspectors that was heading there Thursday to assess its safety.

A team from the International Atomic Energy Agency, led by its director Rafael Grossi, set off for the Russia-held nuclear power plant — Europe's largest — despite the heavy shelling for which Ukraine and Russia trade blame.

Ukraine's Enerhoatom said Russian mortar shelling led to the shutdown of one of its reactors by its emergency protection system. Shelling also damaged a backup power supply line used for in-house needs, and one of the plant's reactors that wasn't operating was switched to diesel generators, the company said.

"There has been increased military activity, including this morning until very recently," Grossi said, adding that after being briefed by the Ukrainian military he decided to get moving despite the inherent risks. "But weighing the pros and cons and having come so far, we are not stopping."

He noted that the risks are "very, very high" in the so-called grey zone between Ukrainian and Russian positions, but "we consider that we have the minimum conditions to move."

A spokesman for the IAEA later said that the mission has been delayed on the Ukrainian-controlled side of the frontline for some three hours, adding that Grossi "has personally negotiated with Ukrainian military authorities to be able to proceed and he remains determined that this important mission reaches the ZNPP today."

The Zaporizhzhia plant 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 area.

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.

"We have a very important mission to accomplish," Grossi said, adding that "we are going to start immediately an assessment of the security and the safety situation at the plant."

"I am going to consider the possibility of establishing a continued presence of the IAEA at the plant, which we believe is indispensable to stabilize the situation and to get regular, reliable, impartial, neutral updates of what the situation is there," he said.

The Russian Defense Ministry said Ukrainian forces unleashed an artillery barrage of the area and then sent a group of up to 60 scouts to try to seize control of the nuclear plant.

It said the Ukrainian troops arrived in seven speedboats, landing three kilometers northeast of the plant on the left bank of the Dnieper River and tried to seize it. The ministry said Russian forces "took steps to destroy the enemy," engaging warplanes. Russia's military said its forces also destroyed two barges carrying Ukrainian troops who attempted to land near the plant.

"The provocation by the Kyiv regime is intended to derail the arrival of the IAEA's group at the Zaporizhzhia nuclear power plant," a ministry statement said.

Alexander Volga, head of the Russia-installed Enerhodar city administration, also said the Ukrainian troops that attempted to land were "blocked and destroyed." The administration also said at least three local residents were killed and one injured early Thursday from Ukrainian shelling.

He said the fighting had since abated and no "objective obstacles" remained to prevent the visit by the IAEA team, which had crossed a checkpoint in Russia-controlled territory and was expected to soon arrive in Enerhodar.

Russian Foreign Minister Sergey Lavrov said Moscow expects "impartiality" from the team.

"We are taking all the necessary measures to ensure that the plant is secure, that it functions safely and that the mission accomplishes all of its plans there," he said.

Ukrainian authorities, meanwhile, accused Russia of shelling Enerhodar and the territory of the nuclear power plant in a false flag attack intended to derail the arrival of the IAEA's team.

"We are demanding that Russia stop provocations and offer the IAEA unhindered access to the Ukrainian nuclear facility," said Zaporizhzhia Gov. Oleksandr Starukh.

On Twitter, Ukrainian Foreign Ministry spokesman Oleg Nikolenko accused Russia's army of "heavily shelling the corridor through which the IAEA's mission is supposed to travel from Zaporizhzhia to the nuclear power plant," and called on Russia to allow their safe passage.

Neither side's version of events could immediately be independently verified.

The fighting came as war-torn Ukraine endeavored Thursday to start the new academic year in the best way possible, with civilian areas still under threat of artillery fire and other weaponry — and children still among the victims. Just over half of schools in Ukraine were reopening to in-person education despite the risks.

In other developments:

- A U.S. intelligence assessment said Russia was facing severe manpower shortages as President Vladimir Putin's 6-month campaign in Ukraine rages on.

- North Korea said it was considering sending construction workers to help rebuild parts of Russian-occupied eastern Ukraine that have been battered by the fighting.

- The emergencies agency under the Russia-backed separatist government in the eastern region of Donetsk said 13 emergency responders were killed and nine others were wounded Thursday by Ukrainian shelling in Rubtsi, a village to the east of the city of Izyum in neighboring Kharkiv province. Much of the fighting in recent weeks and months has centered on the area.

- Lavrov, the Russian foreign minister, warned against any action that could be seen as endangering a Russian contingent in neighboring Moldova, which Moscow considers peacekeepers, would be considered like an attack on Russia itself. His comments underlined concerns that Moldova's separatist Transnistria region, could be drawn into the Russia-Ukraine conflict.

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