TOKYO (AFP) - - UN experts on Thursday went for the first time inside a reactor at the world's largest nuclear plant in Japan since it was shut down last year by an earthquake.

The 12 experts from the International Atomic Energy Agency (IAEA) are on the Vienna-based agency's second inspection of the closed Kashiwazaki-Kariwa plant northwest of Tokyo since July's earthquake.

It marked the first time that inspectors were able to enter one of the reactors, which was still off-limits during the last visit in August.

Philippe Jamet, the leader of the IAEA team, which said in August the plant posted no public heath risk, will hold a news conference on Friday after the end of the latest inspections.

Separately, Japan's trade ministry is working to finish its own inspection on the safety of the plant along with a seismic assessment by the end of March, Yagi said.

"The plant will not be able to resume its operation until its safety is fully guaranteed and it passes the government's safety inspections," he said.

A powerful quake measuring 6.8 on the Richter scale hit central Japan on July 16 last year, causing a fire in the section generating electricity for the plant. The nuclear reactors automatically shut down.

The operator, Tokyo Electric Power Co., said water containing a small amount of radiation leaked into the Sea of Japan (East Sea) and radioactive particles blew out of an exhaust pipe filter.

The company came under criticism for initially underreporting the severity of the incident.

Japan is one of the most earthquake-prone nations, experiencing about 20 percent of the world's powerful tremors.

Despite its propensity for earthquakes, Japan relies on nuclear plants for nearly one-third of its power needs as it has virtually no natural energy resources.

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