Rafael Grossi told a special meeting of the International Atomic Energy Agency's board of governors on Wednesday that he is ``gravely concerned'' by the situation.

He said it's ``the first time a military conflict is happening amid the facilities of a large, established nuclear power program.'' That includes the decommissioned Chernobyl plant, scene of the world's worst nuclear disaster in 1986.

Grossi added, according to a text of his comments provided by the IAEA: ``It is also imperative to ensure that the brave people who operate, regulate, inspect and assess the nuclear facilities in Ukraine can continue to do their indispensable jobs safely, unimpeded and without undue pressure.''