(Adds comments by Israeli military, paragraphs 4-5)
TEL AVIV, Oct 12 (Reuters) - Israel and the United States will hold their biggest joint air-defence exercise next week, the Israeli military said, testing missile interceptors that would serve as a strategic bulwark in any showdown with Iran.
The drill, dubbed Juniper Cobra, has taken place every two years since 2001 but now underscores efforts by the Americans to reassure Israel as they and other world powers pursue negotiations to curb Iran's nuclear programme.
An Israeli defence official, speaking on condition of anonymity, said the manoeuvres would begin on Oct. 20, having been postponed from their original Oct. 12 start-date.
But a military spokeswoman, Lieutenant-Colonel Avital Leibovich, said holding the exercise next week did not constitute a postponement.
"The exercise will happen next week in accordance with the original plan," she said.
U.S. forces including 17 naval ships and ground personnel operating the Aegis, THAAD and Patriot missile shields will be meshed with Israel's Arrow II interceptor for the drill, the defence official said.
"It will be the biggest Juniper Cobra ever," the official said, adding the exercise would be overseen by Admiral Mark Fitzgerald, chief of the U.S. Navy's Sixth Fleet, as well as by the commander of Israel's air defence arm.
The U.S. embassy in Tel Aviv had no immediate word on scheduling. In a statement issued last week, it said Juniper Cobra "is not related to or in response to any world events".
Iran denies seeking a nuclear bomb, but the lack of transparency around its designs and Tehran's rhetoric against the Jewish state have stirred fears of war.
Israel, which is assumed to have the Middle East's only atomic arsenal, has hinted at the possibility of attacking Iran if it deems diplomacy a dead end.
But some analysts believe Israel's military limitations, and U.S. resistance to the idea of pre-emptive strikes, may force it into a more defensive posture with the help of its top ally. (Writing by Dan Williams; Editing by Janet Lawrence)
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