An international team of nuclear experts arrived at the Russian-occupied Zaporizhzhia nuclear power plant Thursday, Ukrainian nuclear operator Energoatom said, after weeks of tense negotiations and several delays as they traveled through an active warzone to complete a risky safety mission.

The team arrived at the plant “to conduct indispensable nuclear safety and security and safeguards activities,” the UN’s nuclear watchdog, the International Atomic Energy Agency, said in a tweet.

The visit by the team of 14 experts from IAEA, including its chief Rafael Grossi, comes at a crucial moment for the plant, which has endured constant shelling and raised fears of a nuclear catastrophe ever since the complex was overrun by Russian troops five months ago.

Reuters quoted Grossi as saying that several members of that team would remain behind to maintain a presence at the plant after he returns later this week to Vienna, where the IAEA is headquartered.

The plant weathered fresh rounds of shelling even as the IAEA team was en route on Thursday, with both Russian and Ukrainian officials saying that Enerhodar, the nuclear facility’s home city, had endured a morning of bombardment.

Russian shells hit the plant, said Energoatom, causing equipment failures that forced the shutdown of one reactor and the activation of backup generators at another.

The extent of damage from the strikes was not immediately clear, and there were no reports of heightened radiation levels around the facility. But weeks of repeated strikes in and around the plant, which is controlled by Russian forces but operated by Ukrainian engineers, have set the international community on edge.

Ahead of the visit, Grossi said the mission was aware of “increased military activity in the area” but was determined to press ahead with its plan to visit the facility and meet personnel there.

Foreign journalists were not permitted to accompany the inspectors, who are among the few international personnel who have crossed the front line since the war began in February, The New York Times reported.

The I.A.E.A. has said that at Zaporizhzhia its team would check on safety systems, assess damage to the plant and evaluate the staff’s working conditions. Among the main concerns is that fires or other damage could cause cooling systems to fail and lead to a nuclear meltdown.

Ukrainian Energy Minister Herman Halushchenko earlier said the mission had a security agreement with Russia, and suggested several members of the team would stay onsite “for several days.”

He added that Ukraine would be unable to ensure the security of the mission while in the plant, as it is Russian-held, and he stressed that situation around the nuclear facility remains “a mess,” CNN reported.

A prolonged IAEA presence at the nuclear plant would likely help to stave off the possibility of a dangerous nuclear accident. Russia would welcome a permanent IAEA presence at the facility, Mikhail Ulyanov, Moscow’s diplomat to the agency, said earlier this week.

“We hope that the visit of the IAEA mission to the station will dispel numerous speculation about the (allegedly) unfavorable state of affairs at the Zaporizhzhia nuclear power plant,” Ulyanov was quoted as saying.

Ukraine’s President Volodymyr Zelensky has previously said that he wants the IAEA to help strike a deal that would demilitarize Zaporizhzhia, rather than simply inspect the plant.

Russian Foreign Minister Sergey Lavrov claimed on Thursday that Russia was doing everything it could so that the IAEA mission could safely carry out its work.