U.N. inspectors head to Zaporizhzhia nuclear plant in Ukraine

International inspectors were heading Monday to the Ukrainian nuclear plant at the center of growing alarm about a potential radiation disaster.

The United Nations nuclear watchdog mission is set to arrive at the Russian-occupied Zaporizhzhia power plant later this week, offering hope for progress even as the two warring sides exchanged new accusations of shelling around the complex in southern Ukraine.

“The day has come,” Rafael Grossi, the head of the U.N.'s International Atomic Energy Agency, said in a tweet early Monday, announcing that a team was "on its way" after weeks of negotiations about getting nuclear inspectors access to the site near the conflict's front lines.

“We must protect the safety and security of Ukraine’s and Europe’s biggest nuclear facility,” he said.

The mission, which will be led by Grossi, will assess physical damage to the plant, determine how well its safety systems are functioning, evaluate working conditions for its staff and perform any urgent safeguard activities, the IAEA said in a separate tweet.

The inspectors are expected to arrive in Zaporizhzhia as early as Wednesday, two people with knowledge of the matter told NBC News.

After making their way from Kyiv, the individuals said, the group will meet with local officials in Zaporizhzhia, in addition to their site visit to the nuclear plant, which is located in nearby Enerhodar. They said the inspectors are expected to spend several days inspecting the power plant.

The U.N.’s atomic energy agency has warned for months about the risk of a nuclear catastrophe, and has sought to send in a team to inspect and help secure the safety of the plant.

Kremlin spokesman Dmitry Peskov said Monday that Moscow considers the mission necessary, the Russian state news agency Tass reported.

He was quoted as saying that Russia will ensure the safety of the IAEA inspectors on the territory that it controls, but reiterated Moscow's opposition to creating a demilitarized zone around the plant. It's up to the international community to pressure Kyiv to reduce tensions around the site, he added.

Ukrainian Foreign Minister Dmytro Kuleba said Monday that the mission "will be the hardest in the history of IAEA" given the active fighting on the ground. Kuleba said earlier that the inspectors were expected to arrive in Kyiv Monday.

Last week, fighting in the area temporarily disconnected the plant from Ukraine’s power grid for the first time in its 40-year history, with President Volodymyr Zelenskyy saying the incident left the world narrowly avoiding a radiation catastrophe.

On Friday, Ukrainian authorities began distributing iodine tablets to residents near the plant in case of any future radiation leak, bringing back painful memories in a country still haunted by the 1986 nuclear disaster at Chernobyl.

Ukraine’s allies have urged Russia to hand over control, and the U.N. has warned that any attack on the plant would be "suicidal."

Kyiv and Moscow have been trading blame for shelling at the plant for weeks. NBC News could not verify either side’s claims.

The Zaporizhzhia plant has been under Russian control since the Kremlin's forces seized land in the south in March, but Ukrainian engineers continue to operate it.

Ukraine’s state nuclear agency, Energoatom, said earlier Monday that Russia “increased pressure” on the station’s personnel ahead of the IAEA mission’s arrival in order “to prevent them from disclosing evidence of the occupiers’ crimes at the plant and its use as a military base.” It did not provide any evidence for the claim.

In its latest update Sunday, the IAEA said that despite reports of renewed shelling in recent days, all safety systems remained operational and there had been no increase in radiation levels.

The United States accused Russia of failing to acknowledge the “grave radiological risk” at the plant, and blocking the final draft of a review of a key U.N. nuclear nonproliferation treaty over the issue.

The news of the mission to Zaporizhzhia was welcomed by the Group of Seven countries, which includes the U.S. In a statement released Monday, it said the IAEA staff must be able to access all nuclear facilities in Ukraine “timely, safely and without impediment.”

It came as Ukraine appeared to launch its long-awaited counteroffensive against Russian-occupied areas in the south, including the Kherson region.

“Today we started offensive actions in different directions,” southern military command spokesperson Natalia Humeniuk told Ukraine’s public broadcaster Suspilne.

Military observers have been anticipating a counterattack on the ground in the south for months as Kyiv seemingly targeted Russian weapons depots and other military installations behind its defensive lines there and in nearby Crimea, annexed by Moscow in 2014.