ZAPORIZHZHIA, Ukraine (AP) -- A U.N. inspection team arrived at Ukraine's Zaporizhzhia nuclear power plant Thursday on a mission to safeguard it from catastrophe, reaching the site amid fighting between Russian and Ukrainian forces that prompted the shutdown of one reactor and underscored the urgency and danger of the task.
The visit from the 14-member expert delegation from the International Atomic Energy Agency came after months of negotiations to get inside Europe's biggest nuclear plant. Arriving in a convoy of SUVs and vans, the inspectors were led by IAEA director Rafael Grossi.
As the experts made their way toward the complex, Russia and Ukraine accused each other of shelling the area and trying to derail the visit. The heavy shelling delayed the team's progress toward the plant.
Energoatom, Ukraine's state nuclear power company, said Russian mortar shelling had led to the shutdown of one of its reactors by its emergency protection system and had damaged a backup power supply line used for in-house needs. One of the plant's reactors that wasn't operating was switched to diesel generators, Energoatom said.
"There has been increased military activity, including this morning until very recently," Grossi said during the journey, adding that after being briefed by the Ukrainian military he decided to keep moving despite the risks. "Weighing the pros and cons and having come so far, we are not stopping."
Grossi, who personally negotiated with Ukrainian authorities to allow the team's passage, noted earlier that the risks were "very, very high" in the so-called gray zone between Ukrainian and Russian positions, but "we consider that we have the minimum conditions to move."
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.
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 briefly 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.
Russia's Defense Ministry said Ukrainian forces unleashed an artillery barrage on the area and then sent a group of up to 60 scouts to try to seize the plant on the Dnieper River. It said that the Ukrainian troops arrived in seven speedboats but that Russian forces "took steps to destroy the enemy," using warplanes.
Russia said some of the Ukrainian shells landed 400 meters (yards) away from the plant's No. 1 reactor.
The Russian-installed administration in the city where the plant is situated, Enerhodar, said at least three residents were killed early Thursday by Ukrainian shelling.
Ukrainian officials, meanwhile, accused Russian forces of shelling Enerhodar and a corridor that the IAEA team was set to go through.
Neither side's version of events could immediately be independently verified.
The fighting came as Ukraine endeavored to start the new school year in the middle of a war. Just over half of the country's are reopening to in-person classes despite the risks.
In other developments, authorities with the Russian-backed separatist government in the eastern region of Donetsk said 13 emergency responders were killed by Ukrainian shelling in Rubtsi, a village in neighboring Kharkiv province. Much of the fighting in recent weeks and months has centered on the area.