Gunmen opened fire on a checkpoint in northern Mosul (search), killing six Iraqis on Monday, while in southern Iraq, attackers ambushed a group of Shiite pilgrims heading to a major religious festival — the latest sign of violence targeting the gathering that draws some 1.5 million people.

In Mosul, four insurgents got out of a car near the checkpoint and began shooting, killing the six victims and wounding eight others, police official Ahmed Mohamed KHalaf Al-Jibori said. U.S. military officials didn't immediately have information on the attack.

Also Wednesday, a car bomb exploded near a U.S. convoy in Baghdad's Abu Ghraib (search) neighborhood, police Lt. Akram Al-Zawobaie said. U.S. military officials said coalition soldiers were not injured.

South of the capital, gunmen opened fire on Shiite pilgrims, killing one and injuring two, police Capt. Muthana al-Furati said.

They were among thousands of Shiites filling roads across Iraq as they headed to Karbala to celebrate the al-Arbaeen religious festival on Thursday. The holiday marks the end of a 40-day mourning period for one of the Shiite religion's most important saints, the grandson of Islam's Prophet Muhammad, Imam Hussein, who was killed in a seventh-century battle.

Officials have feared violence during the gathering, with two attacks against pilgrims reported Monday.

During one, in Musayyib, 40 miles south of Baghdad, a homicide bomber on a bicycle blew himself up near a police patrol protecting pilgrims, killing two policemen.

The other bombing took place at the Imam al-Khedher shrine compound in Khalis, 50 miles north of Baghdad. That attack killed a pilgrim and wounded two other people.

Also Wednesday, gunmen attacked one of the leading Kurdish party buildings, injuring two guards in Mosul, 225 miles north of Baghdad. An attacker was killed by return fire, said Abdul Al-Ghani Botani of the Patriotic Union of Kurdistan.

Iraqi police in the northern part of the country reported the arrest of a leading member of the feared militant group Ansar al-Sunnah Army.

Police forces captured Mohammed Abed, also known as Mohammed al-Hawijy, during a raid late Tuesday near Hawija, 150 miles north of Baghdad, Col. Sarhad Qader said.

In the northern city of Tal Afar, the U.S. military said, soldiers attacked an insurgent vehicle Tuesday, killing one insurgent and injuring another. Numerous weapons were found, the military said in a statement.

Negotiators facing an impasse in the debate over who will lead the country's new parliament worked to try to reach an agreement Wednesday, a day after a chaotic parliament session in which lawmakers shouted at each other and kicked out the media.

The Shiite-led United Iraqi Alliance party, along with the Kurdish coalition, want a Sunni Arab to take the parliament speaker post to heal rifts with the minority Sunnis dominant under former dictator Saddam Hussein. Many Sunnis boycotted the Jan. 30 elections or simply stayed home because they feared attacks at the polls.

Officials lobbied a prominent Sunni Arab leader, interim President Ghazi al-Yawer, to take the job. But he held out for one of two vice presidential spots.

Some politicians speculated that the delay could force them to request a six-month extension to the Aug. 15 deadline for drafting the country's permanent constitution.

The assembly still needs to name an Iraqi president and two deputies, who will in turn nominate a prime minister. The presidency is expected to go to Kurdish leader Jalal Talabani and the premiership to Shiite politician Ibrahim al-Jaafari.

Negotiations over the top posts in the different ministries also continues, with both the Kurds and Shiites vying for the Oil Ministry position. Some Sunnis hope to get the Interior Ministry post, but the Alliance wants them to have the Defense Ministry position instead.

Together, the Alliance and the Kurdish coalition have 215 seats in the 275-seat National Assembly — enough to push through their proposals. But they have been reluctant to alienate the Sunni Arabs and other minority groups, saying they want an inclusive government.