L'AQUILA, Italy, July 9 (Reuters) - French President Nicolas Sarkozy warned Israel on Thursday that any strike against Iran would be catastrophic for the world and told Tehran to expect more sanctions if it refused to discuss its nuclear programme.

Major powers meeting in Italy have given Iran until September to accept negotiations, but were vague about the possible consequences if it failed to do so.

Western countries believe Iran is trying to build an atomic bomb. Tehran says it developing nuclear technology to generate electricity and has so far rejected all overtures for talks.

There has been constant speculation that Israel might attack Iran to try to destroy its nuclear installations, with U.S. Vice President Joe Biden saying earlier this week that Israel had a sovereign right to decide what were its best interests.

Sarkozy urged against any military action.

"A unilateral attack (by Israel) would be an absolute catastrophe," he told reporters during the annual summit of the Group of Eight rich nations.

"Israel should know that it is not alone and should follow what is going on calmly," he said, adding that he had not received any assurances that Israel would hold off on any action ahead of the September deadline.

Sarkozy said patience with Iran was running thin.

"For the past 6 years we have extended our hand saying stop your nuclear armament programme ... Do they want discussions or don't they want them? If they don't, there will be sanctions," he told reporters.

Russia blocked Western countries at the G8 from immediately pushing for further sanctions. (Writing by Crispian Balmer)

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