A team of UN nuclear inspectors has begun assessing a nuclear power plant that was severely damaged by an earthquake last month.
The magnitude-6.8 quake in Niigata prefecture on July 16 caused many malfunctions and leaks at the plant - the world's largest in terms of capacity - and raised concerns about safety at Japan's nuclear power stations.
It also killed 11 people and injured more than 1,000.
The International Atomic Energy Agency (IAEA) team, led by Philippe Jamet, the director of its Nuclear Installation Safety Division, started the four-day assessment on Monday morning.
The team will return to Tokyo on Friday for talks with Japanese nuclear safety officials, Japan's Nuclear and Industrial Safety Agency said.
Jamet said he hoped to receive explanations of all the problems that occurred and inspect the facilities first hand, Kyodo News agency reported.
Jamet told reporters after his arrival on Sunday that his team would conduct an independent examination and then write a report.
Japanese officials, already at the plant for investigations, will co-operate with the six-member IAEA team, but the UN agency's probe will be independent, agency officials said.
Plant operator Tokyo Electric Power Co has come under fire for poor readiness and downplaying safety risks after the quake.
The company revealed hundreds of problems and damages in the quake's aftermath, including a leak of radioactive water into the sea, although the amount of radioactivity released was minimal.
Plant officials said they had not foreseen such a powerful quake hitting the facility, and repeatedly underreported its impact afterward.