Baghdad, Iraq ? A car bomb exploded next to a U.S. Army convoy in Baghdad on Tuesday, killing three soldiers, while another American died in a drive-by shooting a half-hour later. Their deaths pushed the number of U.S. troops killed in three days to 14, part of a surge in attacks that have also killed about 60 Iraqis.

In the northern city of Tal Afar, there were reports that militants were in control and that Shiites and Sunnis were fighting in the streets, a day after two car bombs killed at least 20 people. Police Capt. Ahmed Hashem Taki said Tal Afar was experiencing “civil war.” Journalists were blocked from entering the city of 200,000.

Eighteen U.S. troops have been killed in Iraq during the past week, raising concerns that insurgents may again be focusing their sights on American forces in addition to Shiites.

The deaths come as American troops are trying to pave the way for a graceful exit from Iraq by giving more responsibility to the country’s security forces. But with the Iraqis still relatively weak, U.S. troops remain in the firing line, targeted by insurgents that have shown increasing abilities to attack when and where they please.

More than 620 people, including 58 U.S. troops, have been killed since April 28, when insurgents launched a bloody campaign after Prime Minister Ibrahim al-Jaafari announced his new Shiite-dominated government. The Associated Press count is based on reports from police, hospital and military officials.

During the same period, there have been at least 89 car bombs killing at least 355 people, according to the AP count. There were an additional five suicide bombings by individuals wearing explosives that killed at least 107 people.

Women grieve Tuesday as they comfort a small boy whose mother was killed near the Abul-Fadl Abbas Shiite mosque in Mahmoudiya, which was the target of a car bomb Monday night killing at least 10 people and wounding 30 at about the time worshippers would go to a mosque for sunset prayers.

Also Tuesday, Sunni and Shiite clerics and politicians intensified efforts to find a way out of a sectarian crisis that threatens a civil war.

Senior officials representing Iraq’s two leading Sunni Muslim organizations met with Interior Minister Bayan Jabr. The Sunni officials recently had demanded Jabr’s resignation, holding his office responsible for the killings of Sunni clerics and others.

Abdul-Aziz al-Hakim, a prominent Shiite politician, said there will be no civil war. “The awareness of the Iraqi people and the links between them will prevent such a war, God willing,” al-Hakim told the AP in an interview.

Al-Hakim, who leads both the Supreme Council for the Islamic Revolution in Iraq and the governing United Iraqi Alliance, said insurgents had been trying to start a civil war between the Shiite majority and the Sunni minority since Saddam’s ouster.

The attacks, al-Hakim said, were “the last card in order to incite sectarian war.” He pointed to three against Shiites on Monday, which claimed most of the nearly 50 lives lost on that day alone.