Russia caused a "real danger of a nuclear and radioactive catastrophe" by launching attacks in which all Ukraine's nuclear reactors were disconnected from the power grid for the first time in 40 years, Ukraine's nuclear energy chief said.

Petro Kotin, head of nuclear power company Energoatom, said in a statement on Thursday the vast nuclear power plant in the Zaporizhzhia region had been reconnected to the national power grid after Russian air strikes on Wednesday, and that the backup diesel generators at the site had been turned off. (Reporting by Tom Balmforth, Dan Peleschuk, Pavel Polityuk, Editing by Timothy Heritage)