A second, the official said, was to send a clear message to the United States and other countries that Israel was prepared to act militarily if diplomatic efforts to stop Iran from producing bomb-grade uranium continued to falter.
But American officials were also told that Israel had prepared plans for striking nuclear targets in Iran and could carry them out if needed.
"They are clearly nervous about this and have their air defense on guard," a Bush administration official said of the Iranians.
Two sets of advance Russian-made radar systems were recently delivered to Iran. The radar will enhance Iran's ability to detect planes flying at low altitude.
Mike McConnell, the director of national intelligence, said in February that Iran was close to acquiring Russian-produced SA-20 surface-to-air missiles. American military officials said that the deployment of such systems would hamper Israel's attack planning, putting pressure on Israel to act before the missiles are fielded.
Iran is getting nervous about aircraft fying in the air corridors adjacent to their air space. Israel is making arrangments to remove the nuclear sites in Iran.
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