The operator at the crippled Fukushima Dai-ichi nuclear plant in Japan says damage to its reactors may have caused cracks in the containment vessels equivalent to a 10-centimeter hole, according to NHK news agency.

The March 11 earthquake and tsunami likely created holes and cracks at the bottom of the pressure vessels protecting the reactor cores and damaged the containment vessels, according to the news agency.

Three reactors suffered nuclear fuel meltdowns following the powerful quake and tsunami.

This new data comes as the head of a United Nations nuclear fact-finding mission said Wednesday he has no concerns about working with the Japanese government as his team investigates what happened at the nuclear plant.

Michael Weightman, who is also Britain's top nuclear safety inspector, says the mission is receiving full cooperation from the government and answers to all its questions.

The team was organized by the International Atomic Energy Agency and arrived in Japan on Tuesday. The experts met with government officials on Wednesday, including Chief Cabinet Secretary Yukio Edano.

They are to travel to disaster-affected northeastern Japan on Thursday for visits to the Fukushima Dai-ichi power plant and two other nuclear plants.

The Associated Press contributed to this report.