Three nuclear reactors at a Japanese nuclear plant suffered meltdowns within days, the plant’s operator said on Tuesday.

The disclosure of the meltdown came after a U.N. nuclear safety team began an investigation two months after the quake.

We are here to gather information and to see how we can learn lessons from the unfortunate events,” Michael Weightman, leader of International Atomic Energy Agency (IAEA) team told Reuters.

Engineers are working hard to bring the plant under control and to stop the radiated water leaking from the reactors.

Before traveling to Fukushima, representatives of the IAEA team, which includes nuclear safety experts from France, Russia, China and the United States, will meet Japanese officials this week.

U.N. agency team will prepare a report that will represent the first outside audit of Japan's emergency at a meeting of international officials next month in Vienna.

The government and outside experts had reported that fuel rods at three of the reactors had melted in the early days of the disasters.

The statement renewed the questions whether the officials had been informative about the extent of the crisis, which spread fear of radiation contamination around the world.

“The new exposure indicates that earlier official assessments might have been too optimistic, said Goshi Hosono, an aide to Prime Minister Naoto Kan.

The radiation leaking from the nuclear plant is at a lower level than it was in the early days of the crisis.