The experts’ convoy of armored S.U.V.s traveled toward an active battlefield.

KYIV, Ukraine — Experts from the United Nations’ nuclear watchdog agency are expected to visit the imperiled Zaporizhzhia Nuclear Power Plant on Thursday, a day after they embarked on one of the most complicated missions in the agency’s history.

The group, which includes 14 experts with the International Atomic Energy Agency, left Kyiv, the Ukrainian capital, early Wednesday morning in a convoy of armored S.U.V. vehicles and traveled south. Hours after they departed Kyiv, a Russian official said Moscow would support plans for the inspectors to set up a permanent presence at the facility.

The plant, which is controlled by Russian forces but operated by Ukrainian engineers, is in the middle of an active battlefield where frequent shelling has raised fears of a nuclear catastrophe.

On Wednesday afternoon, the nuclear inspectors reached the Ukrainian-controlled city of Zaporizhzhia, which lies across the Dnipro River from the plant, and they were expected to cross into Russian-held territory on Thursday morning.

“As you know, we have a very, very important task there to perform, to assess the real situation there, to help stabilize the situation as much as we can,” the I.A.E.A. director general, Rafael M. Grossi, told reporters in Kyiv before departing.

Mr. Grossi said the mission had secured safety guarantees from both the Russian and Ukrainian militaries, though dangers lingered. “We are going to a war zone,” he said, “we are going to occupied territory.”

Russian officials have ignored pleas to withdraw from the facility to create a demilitarized zone around it. Fighting is intensifying in the south, where Ukraine is escalating strikes in what could be part of a broader counteroffensive.

It was unclear how long the inspectors would spend at the plant, or how quickly Moscow’s forces would allow them to pass through checkpoints into Russian-held territory.

Moscow’s envoy to the I.A.E.A, Mikhail Ulyanov, wrote in a tweet that Russia “welcomes” the agency’s objective of setting up a permanent presence for international inspectors at the plant, though it remained unclear when such a mission would begin.

Earlier in the day, however, the Russian-appointed head of the Zaporizhzhia region, Yevhen Balytskyi, said the visit was expected to last only one day, calling the delegation’s stated goal for the visit vague.

“They have one day to inspect the operation of the plant,” he said, adding, “If they say some elements need to be attended to, we’ll be able to do so.”