The United Nations atomic agency Tuesday confirmed that Japanese authorities had provisionally raised the severity level for the accident at the Fukushima Daiichi nuclear power plant that was damaged in last month's earthquake to 7, the same level given to the 1986 Chernobyl accident.

The plant suffered major damage from the earthquake and tsunami that struck the country on 11 March and has been spewing radioactive contamination into the environment ever since.

Denis Flory, IAEA Deputy Director General and Head of the Department of Nuclear Safety and Security, told a news conference in Vienna that the re-evaluation of the rating on the International Nuclear and Radiological Event Scale (INES) resulted from an estimate of the total amount of radioactivity released to the environment from the nuclear plant.

The new provisional rating considers the accidents that occurred at Units 1, 2 and 3 of the plant as a single event on INES. Previously, separate INES Level 5 ratings had been applied for Units 1, 2 and 3. The provisional INES Level 3 rating assigned for Unit 4 still applies.

"NISA [The Japan Nuclear and Industrial Safety Agency] estimates that the release of radioactive material to the atmosphere is approximately 10 percent of the Chernobyl accident, which is the only other accident to have an INES rating of 7," he stated.

At the same time, he pointed out that "the Fukushima accident and Chernobyl are very different. Chernobyl happened at a reactor at power. It was a huge explosion… then you had a huge graphite fire for a number of days. Also [Chernobyl had] the power to move all this radioactivity in the high atmosphere and then spread it all around the Earth."

The INES scale, developed jointly in 1990 by the IAEA and the nuclear energy agency of the Organization for Economic Co-operation and Development (OECD), is a way to communicate the significance of nuclear and radiological events to the public.

Flory explained that the "below scale" is for events which have no safety significance, while those meeting the criteria for the first three levels are rated as "incidents" and the last four levels as "accidents."

The highest, Level 7, is used to describe an event comprised of "a major release of radioactive material with widespread health and environmental effects requiring implementation of planned and extended countermeasures."

He said that, overall, the situation at the plant remains "very serious," but there are early signs of recovery in some functions such as electrical power and instrumentation.

Meanwhile, NISA has confirmed that no changes were observed on the readings at the on-site radiation monitoring posts following the 6.6 magnitude quake that struck Fukushima prefecture on Monday.