The sons of Iraq's top Shiite cleric and two other grand ayatollahs met Monday with radical cleric Muqtada al-Sadr (search), telling him they oppose any U.S. assault to capture him, a man who attended the meeting told The Associated Press.

The rare gathering reflected the depth of Shiite Muslims fears of military action in Najaf, their holiest city. The top cleric, Grand Ayatollah Ali al-Husseini al-Sistani (search) — a moderate who opposes anti-U.S. violence — has long kept the young, vehemently anti-American al-Sadr at arm's length.

"They agreed not to allow any hostile act against Sayyed Moqtada al-Sadr and the city of Najaf," said the man in the meeting, speaking on condition of anonymity.

He said the meeting took place in al-Sadr's office, where his supporters said he moved to from Kufa several days ago and where he has remained holed up, surrounded by armed militiamen.

U.S. troops have been seen on the outskirts of Najaf, and the top American general in Iraq said Monday the military aimed to kill or capture al-Sadr, whose al-Mahdi Army (search) militia launched an uprising across the south last week against coalition troops.

Members of Iraq's Governing Council and Shiite political parties have launched negotiations with al-Sadr, hoping to avert military action. Persuaded to meet one U.S. demand, Al-Sadr withdrew his militiamen Monday from police stations they seized in Najaf and the nearby cities of Kufa and Karbala and allowed police to return.

Al-Sistani's son, Mohammed Rida, often serves as his main envoy: The 75-year-old grand ayatollah never leaves his home, which is not far from al-Sadr's office.

The elder al-Sistani is immensely popular among Iraq's Shiite majority, while most Shiites have shunned the 30-year-old al-Sadr, a lower-level cleric seen by many as too young and too radical.

But the unexpected strength shown by al-Sadr's al-Mahdi Army militia in last week's uprising has increased his influence, and the prospect of a U.S. military operation in Najaf is alarming to Iraq's Shiites.

Al-Sadr office is a stone's throw from the Imam Ali Shrine (search), raising the possibility of damage to the holiest Shiite site in Iraq if he is targeted in an attack. The shrine also is the third holiest in the world after Mecca and Medina in Saudi Arabia.

Under an agreement with Shiite leaders in Najaf, coalition troops do not enter the area around the shrine because of religious sensitivities.

Few of the black-garbed gunmen of al-Mahdi Army were seen in Najaf's streets Monday, except around the shrine area.

The pullback by al-Sadr appeared to be an attempt to avert U.S. action, though al-Sadr followers rejected another U.S demand — the dissolution of the al-Mahdi Army.

The U.S. military wrested the southern city of Kut from al-Mahdi Army control over the weekend, when hundreds of U.S. troops entered the city in the first major American military foray into the south in months.

In cities further south, the militia's uprising has been largely tamed after gunmen battled coalition forces in fierce fighting early last week. Italian troops blew up the al-Sadr offices in Nasiriyah late Sunday after securing it earlier from militiamen.