VIENNA, Aug 17 (Reuters) - A Japanese reactor hit by an earthquake last month performed safely during and after the quake, but some of its components could be affected by hidden damage, the U.N. nuclear watchdog said on Friday.

The Kashiwazaki Kariwa nuclear power plant, the world's largest, suffered low-level leaks of radioactive material when a 6.8 magnitude quake struck on July 16 -- a quake that significantly exceeded the seismic input taken into account when the plant was designed, according to the International Atomic Energy Agency (IAEA).

"The installation behaved in a safe manner," the IAEA said in a report published on Friday.

Yet while the structures, systems and components of the plant, run by Tokyo Electric Power Co. (TEPCO) <9501.T>, seemed to be in a much better general condition than might be expected, the examination was not yet finished, the IAEA said.

"Important components like the reactor vessels, the core internals and the fuel elements have not yet been examined and in-depth inspections are still to be performed," the IAEA said.

Non-safety related structures, systems and components were suffered significant damage from factors such as soil deformation and oil leakages, the IAEA said.

"Another consideration is the possibility that long term operation of components could be affected by hidden damage from this event," the report said.

"A re-evaluation of the seismic safety the Kashiwazika Kariwa nuclear power plant needs to be done with account taken of the lessons learned from the... earthquake and using updated criteria and methods."

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