Israel on Wednesday said it had foiled an "advanced" al-Qaida plan to carry out a suicide bombing on the U.S. Embassy in Tel Aviv and bomb other targets, in what analysts said was the first time the global terror network's leadership has been directly involved in plotting an attack inside Israel.

The Shin Bet intelligence agency said it had arrested three Palestinians who allegedly plotted bombings, shootings, kidnappings, and other attacks. It said the Palestinian men, two from Jerusalem and one from the West Bank, were recruited by an operative based in the Gaza Strip who worked for al-Qaida leader Ayman al-Zawahiri.

Washington said the United States was not yet able to corroborate the Israeli claims.

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While a number of groups inspired by al-Qaida have carried out attacks against Israel before, this appeared to mark the first time an attack was directly planned by al-Qaida leaders.

The Shin Bet said the Palestinians planned on attacking a Jerusalem conference center with firearms and then kill rescue workers with a truck bomb. Al-Qaida also planned to send foreign militants to attack the U.S. Embassy in Tel Aviv on the same day using explosives supplied by the Palestinians, it said.

It said five men whose identity and nationality were not disclosed were to fly into Israel with fake Russian passports to attack the American embassy. It was not clear where the men are located.

The Palestinian operatives had planned on several other attacks, it said. One included shooting out the tires of a bus and then gunning down passengers and ambulance workers.

The agency said the plot was in "advanced planning stages," but gave no further information on how close the men got to carrying it out. It said the Palestinians from Jerusalem had used their Israeli resident cards to scope out and gather intelligence on targets. They were arrested in the past few weeks, it said.

A number of al-Qaida inspired groups have carried out rocket attacks from Gaza and Egypt's Sinai Peninsula, as well as shootings in the West Bank. Israeli intelligence calls these groups part of a "global jihad" movement.

Aviv Oreg, a former head of the Israeli military intelligence unit that tracks al-Qaida, said the plot marked the first time it has been directly linked to an attempted attack in Israel.

"This is the first time that Ayman al-Zawahiri was directly involved," he said. "For them, it would have been a great achievement."

The Shin Bet said the three suspects made contact with al-Qaida over the Internet. It said they planned on traveling to Syria — where various jihadist groups are battling the forces of President Bashar Assad — for training.

Oreg said that many foreign fighters fighting the Assad regime are from Chechnya and predominantly Muslim parts of Russia and speculated that the militants with the phony documents would be from there.

Al-Qaida inspired groups are on the rise in the Gaza Strip, which is run by the Islamic militant Hamas.

These groups accuse Hamas of being too lenient because it has observed cease-fires with Israel and has stopped short of imposing Islamic religious law, or Shariah, in Gaza.

In the West Bank, Israel and the Palestinian Authority of Western-backed Palestinian President Mahmoud Abbas have cracked down on Islamic militants. Three Salafis, members of a movement that advocates a hard-line interpretation of Islamic law, were killed in a shootout with Israeli soldiers in the West Bank last November.

In Washington, State Department spokeswoman Marie Harf said U.S. investigators and intelligence officials were not yet able to corroborate the Israeli information and declined comment on specifics of the case.

"Obviously we're looking into it as well," Harf told reporters Wednesday. "I don't have reason to believe it's not true. I just don't have independent verification."

She said there were no plans to evacuate the U.S. Embassy in Tel Aviv and was not immediately aware of stepped-up security measures there in light of the arrests.