International Atomic Energy Agency chief Rafael Grossi will lead a mission to Chernobyl as soon as possible, he said on Friday, after Ukraine said Russian troops had left the radioactive waste facilities there though some remained nearby.

"I will head an (IAEA) assistance and support mission to (Chernobyl) as soon as possible. It will be the first in a series of such nuclear safety and security missions to #Ukraine," Grossi said on Twitter. 

He is due to hold a news conference at 1230 GMT.