TEHRAN, Sept 6 (Reuters) - A senior Iranian official accused the United States on Thursday of supporting Kurdish separatist rebels operating in western border areas, the official IRNA news agency reported.

"America has become so weak so that it is trying to strengthen bandits and small groups like PJAK to carry out actions such as blowing up Iran's oil pipelines," Ali Larijani, secretary of Iran's Supreme National Security Council, said.

Larijani, who did not give details of any attacks on Iranian oil pipelines, was speaking two days after another Iranian official was reported to have denied Iraqi accusations that Iran had been shelling Kurdish areas in neighbouring Iraq.

PJAK, the Party of Free Life of Kurdistan, is an Iranian offshoot of the Kurdistan Workers Party (PKK), a Kurdish separatist movement that is fighting Turkey.

PJAK guerrillas, who seek autonomy for Kurdish areas in Iran, are thought to shelter in northeastern Iraq.

Cross-border clashes occasionally occur as Iran and Turkey battle rebels operating from bases in Iraq's mountainous northeastern region of Kurdistan.

Iran has also previously accused the United States and Britain of supporting ethnic minority rebels operating in sensitive border areas in an attempt to destabilise the country.

For their part, U.S. officials say Iran is fomenting violence in Iraq. Nevertheless, U.S. and Iranian officials have held talks on Iraq in Baghdad since May, the most high profile meetings since ties were cut after the 1979 Islamic revolution.

Ties between Iran and Iraq, both mainly Shi'ite Muslim, have improved since 2003 when U.S. forces toppled Saddam Hussein, a Sunni Muslim who waged an eight-year war with Iran in the 1980s.

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