Nuclear power is safer around the world than it was a year ago at the time of the Fukushima disaster in Japan, the head of the UN atomic agency said Monday, while warning against complacency.

"Next Sunday it will be exactly one year since this very serious accident. We have come a long way in that time," International Atomic Energy Agency head Yukiya Amano told a news conference at its Vienna headquarters.

"Nuclear power is now safer than it was one year ago. But nuclear safety is something that must be well kept every day and we must never become complacent," Amano, himself Japanese, said during a quarterly IAEA board meeting.

He said that the Fukushima nuclear crisis, the world's worst in 25 years, was sparked by a huge earthquake and tsunami on March 11 last year, but that there were also "human and managerial failings."

Amano said that "good progress" has been made implementing the IAEA's nuclear safety action plan, involving "stress tests" on nuclear power plants, peer reviews and the strengthening of defences against natural disasters.