BAGHDAD - Militant Shiite cleric Muqtada al-Sadr called yesterday for followers to hold weekly protests against a U.S.-Iraqi security deal being negotiated that could lead to a long-term American troop presence.

He also demanded that the deal be put to a popular referendum. He vowed to gather one million signatures rejecting the deal.

Sadr's outcry could sharply heighten tensions over the deal, which is supposed to be finished by July to replace the U.N. mandate that oversees U.S.-led troops in Iraq.

Sadr - whose powerful Mahdi Army militia has often battled U.S. and Iraqi forces - is one of the most vocal opponents of the U.S. presence in Iraq, but many Iraqis have expressed worries over any final deal that involves permanent American bases.

Sadr, who is believed to be in Iran, did not give specific guidance on the planned demonstrations in a statement issued by top Shiite religious officials. Any major marches could put added strain on a tenuous truce between the Mahdi Army and the government of Prime Minister Nouri al-Maliki after weeks of battles that began in late March.

In northern Iraq yesterday, a car bomb exploded near a popular market in Tal Afar, killing four civilians and wounding 46, said the mayor, Maj. Gen. Najim Abdullah.

No one immediately claimed responsibility. The blast came hours after an al-Qaeda in Iraq front group warned that insurgents would retaliate against U.S. and Iraqi forces, which began a crackdown nearly two weeks ago in the northern city of Mosul, 40 miles east of Tal Afar.

A man claiming to be a spokesman for the Islamic State of Iraq in Ninevah province, which includes Mosul, said in a videotape posted online that insurgents were at "full strength" despite the Mosul sweeps and were just waiting for the proper time to counterattack. The Islamic State of Iraq is a coalition of insurgent groups led by al-Qaeda in Iraq.

There was no way to authenticate the comments. But the video bore the logo of al-Furqan, one of al-Qaeda's media production wings, and was posted on a number of Islamic Web sites that usually carry militant statements.

Mosul has been dubbed by the U.S. military as al-Qaeda in Iraq's last major urban stronghold.

Officials have claimed initial success in the crackdown, saying more than 1,200 suspects have been detained. Iraqi security forces also have met with little resistance - though some attacks have occurred, including a shooting near a Mosul police station that killed a policeman yesterday, according to an Interior Ministry spokesman, Maj. Gen. Abdul-Karim Khalaf.

On the political front, Maliki convened a meeting with Iraq's president, the two vice presidents, and other political leaders late Monday to discuss the security-deal negotiations with the United States.

Maliki said the decision "should be shared by all political powers in the country," said Nasser al-Ani, a spokesman for the presidential council. He said the delegates agreed to continue the dialogue.

Details of the terms under negotiation are not known. Maliki has said that the deal would provide for U.S. security help to protect Iraq, and that most Iraqi leaders have said they supported some form of continued American role. But the numbers of U.S. troops and rules of conduct in Iraq remain highly controversial.

On Other Fronts

The State Department

has begun to identify diplomats who could be forced to serve at the American Embassy in Baghdad and in outlying Iraqi provinces next year unless enough volunteers come forward to fill about 300 positions.

Three Iraqis, including

the father of a slain boy, appeared yesterday before a federal grand jury in Washington investigating a deadly Sept. 16 shooting in Baghdad involving Blackwater Worldwide contractors. One of the three was Mohammed Abdul-Razzaq, whose son Ali, 9, was killed in the shooting; he told ABC News before leaving Iraq that he wanted justice for "a crime that needs to be punished." Blackwater, hired to guard U.S. diplomats in Iraq, is not a target of the investigation; the case has focused on as few as three or four guards and whether they acted illegally.

Swedish Prime Minister

Fredrik Reinfeldt urged

the United States and European countries to admit more Iraqi refugees, saying Sweden had borne too much of the burden. Sweden, which opposed the U.S.-led invasion of Iraq, has taken in about 40,000 Iraqis since 2003. The United States admitted just more than 1,600 in fiscal 2007. The Bush administration has said it intends to take in 12,000 by the end of September.

- Associated Press