Electrabel, part of the giant French group GDF-Suez, said Friday it will restart two nuclear reactors closed down in 2012 after micro-cracks were found in them, sparking fears about their safety in the aftermath of Japan's Fukushima disaster.

Belgium's nuclear safety authority, AFCN, "authorises the restarting of the Doel 3 and Tihange 2 reactors," Electrabel said in a statement.

"Electrabel will now make preparations to restart them," it added.

The AFCN said the two reactors "could be restarted in full confidence because all the safety issues ... have been resolved satisfactorily."

It would take two to three weeks to get them back online, it said.

Many "potential cracks" were found during inspections early last year at the base of Doel 3 reactor vessel, near the northern city of Antwerp, which was closed in June, as well as Tihange 2, near the southern city of Liege.

Environmental groups oppose restarting the reactors and have called on the government to delay the move.

Greenpeace said the authorities were "blindly" following the view of the AFCN.

"It is clear -- it is not the government running the country, it is the nuclear industry," Greenpeace said, warning that it would take legal action.