A team of UN nuclear experts has begun a four-day inspection of a Japanese atomic power plant damaged in a powerful earthquake last month.
The IAEA wants to learn what happened at the power plant
The operators of the Kashiwazaki-Kariwa power station have admitted there were leakages of radioactive material.
But the Tokyo Electric Power Company said there was no danger to the public.
The visit follows a request by the Niigata regional government. Tokyo initially said no international inspection was necessary.
The team from the International Atomic Energy Agency will return to Tokyo on Friday for talks with Japanese nuclear safety officials.
The team's leader, Philippe Jamet, said they will conduct an independent investigation and then file a report.
"Our aim today is to draw lessons from the earthquake that happened here, to share with the international community," said Mr Jamet.
Niigata officials said bringing in outside experts would help to damp down rumours that the radiation leaks had been more serious than admitted.
Unease arose when the leaks were found to have been much bigger than first estimated.
The power company has said getting the plant running again could take some time, because contaminated water needs to be cleaned up first and dozens of other problems need to be fixed.
The magnitude 6.8 earthquake struck in mid-July and caused more than 50 malfunctions at the Kashiwazaki-Kariwa plant.
The quake killed 10 people and injured hundreds.