Those concerns intensified in February after U.N. inspectors revealed their discovery of uranium particles of 83.7% purity at an Iran nuclear facility built deep underground to protect it from air strikes. Western officials fear a nuclear-armed Iran could threaten Israel, Gulf Arab oil producers, and spark a regional arms race. A senior Iranian nuclear official said Tehran would not take the revival of U.N. sanctions lying down. But Western officials and analysts say that Iran's production of 90% uranium would demand a significant response. 'FACE A CRISIS AT SOME POINT'While Western officials want to leave the door open for diplomacy, tensions with Russia and China make that harder.

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