VIENNA - (AP) - The Japanese reactor crisis poses a major challenge with enormous implications for nuclear power, the head of the U.N.'s atomic watchdog said Monday.

Yukiya Amano, head of the International Atomic Energy Agency, also stressed that the global community cannot take a "business as usual approach." Lessons must to be learned from what happened at the Fukushima Dai-ichi plant after it was hit by a massive tsunami and earthquake on March 11 and has been releasing radiation into the environment ever since, he said.

Amano spoke at the opening session of a meeting that has drawn representatives from dozens of countries to scrutinize safety ateach other's power plants.

"I know you will agree with me that the crisis at Fukushima Dai-ichi has enormous implications for nuclear power and confronts all of us with a major challenge," Amano told delegates. "We cannot take a business as usual approach."

The worries of millions of people around the world about the safety of nuclear energy "must be taken seriously," Amano said, and called for transparency and "rigorous adherence to the most robust international safety standards."

"It is clear that more needs to be done to strengthen the safety of nuclear power plants so that the risk of a future accident is significantly reduced," he said.

In other comments, Amano said the IAEA would like to send an international expert mission to Japan as soon as possible to carryout an assessment of the accident.

Looking to the future, he added that arrangements for putting international nuclear experts in touch with each other quickly after incidents like these need to be improved.

"I am confident that valuable lessons will be learned from the Fukushima Dai-ichi accident, which will result in substantial improvements in nuclear operating safety, regulation and the overall safety culture," he said.