(Adds reaction from Niigata governor)

TOKYO, July 21 (Reuters) - Japan has turned down an offer of help from the U.N. nuclear watchdog following last week's quake which damaged the world's biggest nuclear power plant, media reported on Saturday.

Authorities closed down the Kashiwazaki-Kariwa nuclear plant indefinitely after Monday's 6.8 magnitude quake in northwestern Japan caused radiation leaks there. The quake also killed ten people and flattened hundreds of houses.

Mohamed ElBaradei, the head of the International Atomic Energy Agency (IAEA), had offered to send in inspectors, urging Japan to share lessons from the incident.

But Kyodo news agency reported sources as saying Japanese nuclear safety authorities would work by themselves to deal with problems at the plant for the time being, leaving room for possibly seeking an IAEA inspection at a later date.

The governor of Niigata prefecture, where the quake occurred, said IAEA inspectors should come visit the site.

"Withholding an invitation may breed an unintended notion that there may be something wrong," Governor Hirohiko Izumida, was quoted as saying by Kyodo.

He added Japan should host an IAEA team "as soon as possible to show to the world what has happened".

The leaks have renewed fears about the safety of the nuclear industry, which supplies about one third of Japan's power.

Television showed officials from Tokyo Electric Power Co. (TEPCO), the operator of the closed plant, meeting a local government team at the facility on Saturday.

TEPCO has acknowledged that the tremor was stronger than the plant, whose first reactor came on stream more than 20 years ago, had been designed to withstand.

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