Masked Shiite gunmen roamed through west Baghdad?s Jihad neighborhood, dragging Sunnis from their cars, picking them out on the street and killing them in a rampage that police said killed 41 people in a dramatic escalation of sectarian violence.

Hours later, two car bombs exploded near a Shiite mosque in the city's north, killing 17 people and wounding 38 in what appeared to be a reprisal attack, police said. Yesterday, two car bombs exploded nearly simultaneously in a Shiite area of Baghdad, killing at least eight and wounding dozens, police and hospital officials said.

In the northern city of Kirkuk, meanwhile, a suicide truck bomb struck a Kurdish political office, killing four people and wounding seven, police said. The car bombings came a day after masked Shiite gunmen ambushed Sunni Arabs in western Baghdad, a dramatic escalation of sectarian violence that killed 41 people.

First a car parked near a repair shop on the edge of the Shiite slum of Sadr City blew up. Minutes later, a suicide car bomber drove into the crowd that had gathered near the site. Officials at hospitals where the victims were taken said at least eight people were killed and 41 wounded.

In Kirkuk, the truck exploded as it tried to plow through a concrete wall surrounding the complex of the Patriotic Union of Kurdistan, one of the main Kurdish political parties in Iraq. Four people were killed and seven were wounded, police Brig. Sarhat Qadir said.

Meanwhile, black-clad Shiite militiamen manned checkpoints on roads into most major Shiite neighborhoods to guard against revenge attacks, as scattered clashes occurred across the Iraqi capital. Sunni leaders expressed outrage over the killings, and President Jalal Talabani, a Kurd, appealed for calm, warning that the nation stood ?in front of a dangerous precipice.?

Presidential security adviser Wafiq al-Samaraie told Al-Jazeera television that ?we are at the gates of civil war? unless ?exceptional measures? are taken.

A senior government official, Haidar Majid, contested the police figures, saying late Sunday that only nine people died in Jihad. Police Lt. Mohammed Khayoun insisted the figure of 41 was correct ? kwith 24 bodies taken to Yarmouk hospital and 17 to the city morgue. There was no way to reconcile the discrepancy. Regardless, the brazen attack was likely to further enflame Shiite-Sunni tensions and undermine public confidence in Iraq's new unity government. It also raises new questions about the effectiveness of the Iraqi police and army to curb sectarian violence in the capital.

The trouble started about 10 a.m. when several carloads of gunmen drove into the Jihad area along the main road to Baghdad International Airport, police and witnesses said. The gunmen stopped cars, checked passengers' identification cards and shot dead those with Sunni names.

Masked gunmen wearing black clothes roamed the streets, abducting Sunnis whose bodies were found later scattered throughout the religiously mixed neighborhood, an Interior Ministry official said. He spoke on condition of anonymity because he was not authorized to talk to media. US and Iraqi forces sealed off the area, and residents said American troops using loudspeakers announced a two-day curfew. Black smoke from burning tires wafted through the streets.

Another policeman, Lt. Maitham Abdul-Razzaq, also said 41 bodies had been collected and taken to hospitals. Some Sunni clerics put the death toll at more than 50 in Jihad, a once prosperous neighborhood of handsome villas owned by officials of Saddam Hussein's security services. Residents contacted by telephone told of gunmen systematically rounding up and massacring Sunni men.

A Shiite shopkeeper said he saw heavily armed men pull four people out of a car, blindfold them and force them to stand to the side while they grabbed five others out of a minivan. ?After ten minutes, the gunmen took the nine people to a place a few meters (yards) away from the market and opened fire on them,? Saad Jawad al-Azzawi said.

Wissam Mohammad al-Ani, a Sunni, said three gunmen stopped him as he was talking toward a bus stop and demanded his identification. They let him go after he produced a fake ID with a Shiite name, but they seized two young men standing nearby.

Police and Shiite leaders speculated the rampage was carried out in retaliation for a Saturday night car bombing at a Shiite mosque that killed two people and wounded nine. Clashes also broke out between gunmen and Iraqi police in at least three neighborhoods across the capital, police and residents said. Three Shiite militiamen were killed in fighting with security forces in one of them, police said.

The spokesman for a Sunni clerical association, Mohammed Beshar al-Faydhi, blamed the Jihad attack on the Mahdi Army militia, led by radical Shiite cleric Muqtada al-Sadr. Al-Faydhi told Al-Jazeera television that he had documents to prove his allegation. Al-Sadr denied responsibility and called on both Shiites and Sunnis to ?join hands for the sake of Iraq?s independence and stability?. He assured Vice President Tariq al-Hashimi, leader of the largest Sunni Arab party, that he would punish any of his militiamen if they were involved.

Prime Minister Nouri al-Maliki, a Shiite, has promised to disband Shiite militias and other armed groups, which are blamed for much of the sectarian violence. On Friday, Iraqi troops backed by US jets raided a Shiite militia stronghold in Baghdad's Sadr City neighborhood, killing and wounding dozens of people.

But militias have flourished in large part because of the inability of the police, the Iraqi army and coalition forces to guarantee security. Many in the Shiite majority believe the militias are their only protection against Sunni extremists such as al-Qaida in Iraq, responsible for many car bombings and suicide attacks against Shiite civilians.

The violence is likely to complicate US and Iraqi efforts to encourage disaffected Sunnis to abandon the Sunni-dominated insurgency and join mainstream politics so US troops can begin to go home. Deputy Prime Minister Salam al-Zubaie, a Sunni, on his part described the Jihad attack as ?a real and ugly massacre?.