Grossi visited a nuclear power plant in southern Ukraine on Wednesday on his first trip to the country since Russia's invasion raised fears of a nuclear accident.

The head of the International Atomic Energy Agency has repeatedly warned of the dangers of the conflict -- the first in a country with a vast nuclear estate.

"Grossi arrived in Kaliningrad today for talks with senior Russian officials tomorrow morning," the IAEA wrote in a statement late Thursday.

After his visit to Ukraine, the agency was in close consultations with Ukrainian authorities towards sending its first "assistance and support mission" to the Chernobyl nuclear power plant in the next few days, it added.

Grossi was expected to return to the IAEA's headquarters in the Austrian capital Vienna on Friday and hold a press conference later in the afternoon.

Ukraine has 15 reactors at four active nuclear power plants, as well as stores of nuclear waste, including at Chernobyl -- the site of the world's worst nuclear disaster in 1986.

Ukrainian officials said late Thursday that Russians had withdrawn from Chernobyl after weeks of occupation.

Russian forces seized control of the defunct power plant site -- where radioactive waste is still stored -- on February 24, the first day of the invasion.

They also captured Europe's largest nuclear plant at Zaporizhzhia on March 4, sparking alarm when shelling caused a fire at a training facility.