(Reuters) - Israel is upgrading its Arrow II ballistic missile shield in a U.S.-backed "race" against Iran, Syria and other regional enemies, a senior Israeli defense official said on Sunday.

The new "Block 4" generation of guided interceptor rockets, radars and technologies for synchronizing Arrow with U.S. systems was being installed in deployed Israeli batteries, a process that would take several weeks, the official said.

"The accuracy and the reach will be greater," the official said of Arrow, which has been operational since 2000 and is designed to blow up incoming missiles at altitudes high enough for non-conventional warheads to disintegrate safely.

"It is part of the technological race in the region," the official, who declined to be named, told Reuters.

Long jittery about Iran's disputed nuclear program, the Israelis have more recently worried the Syrian insurgency could loosen Damascus's hold on its chemical weapons and missiles.

Israel has threatened to attack preemptively in both countries, a prospect that could trigger wider war and clash with Washington's efforts to resolve the crises diplomatically.

Iran, which denies seeking nuclear weapons, has repeatedly vowed to retaliate against any attack. "(Israel) knows that attacking Iran is an unattainable wish, unless the regime seeks to commit suicide," Iranian Defense Minister Ahmad Vahidi was quoted as saying by the state news agency IRNA on Sunday.

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