A furnace exploded at the Marcoule nuclear waste treatment site in southern France on Monday, killing one person, but there was no leak of radioactive material outside the furnace, France's ASN nuclear safety watchdog said.
Four other people were injured, one seriously, in the blast at the Centraco site, owned by French power utility EDF and adjacent to the Marcoule nuclear research centre. The site does not house any nuclear reactors.
The furnace that exploded is used to melt waste with levels of radioactivity ranging from low to very high, ASN said.
It did not immediately give a reason for the blast but said it was completely contained within the furnace.
Police also said there was no contamination outside the site, which is about 30 km (18 miles) from the city of Avignon and about 80 km (50 miles) from the Mediterranean coast.
"We are now interested in information," Amano told a news conference.
France's main stock market reacted negatively to the explosion. France's share benchmark CAC 40 extended its losses on Monday, down 5 percent after news of the explosion.
At 1208 GMT, the index was down 5.1 percent at 2,823.94 points, while the FTSEurofirst 300 index of top European shares was down 3.6 percent at 882.99 points.
France's ASN nuclear safety watchdog said there was an explosion at the French nuclear site of Marcoule, a nuclear waste management site that does not include any reactors.