The International Atomic Energy Agency (IAEA) said on Tuesday that radioactivity is being released directly into the atmosphere from the Unit 4 reactor at Japan's Fukushima Daiichi plant.

The agency said the Japanese authorities said that the spent fuel storage pond at the Unit 4 reactor of the Fukushima Daiichi nuclear power plant is on fire and radioactivity is being released directly into the atmosphere.

The nuclear watchdog said dose rates of up to 400 millisievert per hour have been reported at the site. The Japanese authorities are saying that there is a possibility that the fire was caused by a hydrogen explosion, the watchdog said in a statement published on its website.