Shiite leader Muqtada al-Sadr on Friday renewed threats to resume attacks on U.S. forces, and the country's top Shiite cleric was quoted as saying he would intervene if a proposed U.S.-Iraqi security pact infringed on Iraqi sovereignty.

The statements deepened unease over the deal, which would allow American troops to stay in Iraq for three more years after their U.N. mandate expires Dec. 31. Iraqi officials say they will seek a renewal of the mandate if the pact is not signed by then.

Al-Sadr's threat came in a statement by the Iran-based cleric that was read to supporters gathered for Friday prayers in Baghdad's Shiite Sadr City enclave and the city of Kufa, south of Baghdad.

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"I repeat my call on the occupier to get out from the land of our beloved Iraq, without retaining bases or signing agreements," al-Sadr said. "If they do stay, I urge the honorable resistance fighters ... to direct their weapons exclusively against the occupier."

The statement did not say exactly when and under what conditions such attacks might resume.

In the holy city of Najaf, an official close to Grand Ayatollah Ali al-Sistani said the Iranian-born cleric has vowed to "directly intervene" if the final version of the agreement breached the country's sovereignty. The official spoke to The Associated Press on condition of anonymity because he is not authorized to speak to the media.

Al-Sistani wields vast influence among Iraq's majority Shiites, and the agreement will virtually have no chance of being passed by parliament if he publicly states his opposition to it.

He has in the past forced the United States to scrap or revise political blueprints for Iraq, sending hundreds of thousands of supporters to the streets in 2004 to back his demand for a general election. The vote was held in January 2005.

His reported threat Friday to intervene over the security pact follows an Oct. 29 statement from his office that said the cleric wanted Iraqi sovereignty to be protected in the agreement. The escalation is likely to rattle Shiite Prime Minister Nouri al-Maliki, who picked the negotiators who worked on the agreement with the Americans.

Al-Maliki's government has sought amendments to the draft agreement to satisfy critics who claim the text does not give strong enough guarantees to safeguard the country's sovereignty and force the Americans to leave by Dec. 31, 2011.

Al-Sadr's Mahdi Army militia launched two uprisings against U.S. forces in 2004 and another one this past spring. In July, al-Sadr said he was disbanding most of the militia, but would keep a small combat unit of seasoned and loyal fighters in case they are called upon to fight the Americans again.

In Friday's statement, al-Sadr for the first time gave that unit a name: The Promised Day Brigade.

He also called on breakaway groups from his militia to join the brigade. He was apparently referring to so-called "special groups," which the U.S. military says are trained and armed by Iran to attack Americans.

Al-Sadr's statement also called on supporters to gather next week for prayers in a central Baghdad square in a show of opposition to the U.S.-Iraqi pact. Tens of thousands of al-Sadr supporters assembled in Baghdad last month to show they oppose the agreement.