Updated

Iraq's interim prime minister warned Monday that the rebels were trying to foment a sectarian war in the country, as thousands of mourners attended funerals in the Shiite holy cities of Najaf (search) and Karbala (search) a day after car bomb attacks killed 67 people.

Interim Prime Minister Ayad Allawi (search) said the mainly Sunni Muslim insurgents, blamed for the deadly strikes Sunday against Iraq's majority Shiites, want to "create ethnic and religious tensions, problems and conflicts ... to destroy the unity of this country."

"These attacks are designed to stop the political process from taking place in Iraq," Allawi told reporters. He added that he expected more such strikes as key Jan. 30 parliamentary elections — the first free vote in Iraq since the overthrow of the monarchy in 1958 — get closer.

Illustrating continuing tensions in the region, a bomb exploded at a police checkpoint in Karbala Monday, causing damage to surrounding buildings but inflicting no casualties. Police said they cordoned off the area and arrested the attacker.

Shiites, who make up around 60 percent of Iraq's population, have been strong supporters of the upcoming electoral process, which they expect will reverse the longtime domination of Iraq by the Sunni minority, the country's other main religious sect. The insurgency is believed to have been fomented by Sunnis, who made up the majority of Saddam Hussein's former Baath Party leadership.

Shiite officials and clerics blamed the Najaf and Karbala bombings — the worst carnage in Iraq since July — on Sunni insurgents wanting to ignite a sectarian war. The strikes appeared designed to cause massive casualties and eventual reprisals by the Shiites against Sunnis.

"We always have said that we are going to fight and defeat terrorism," Allawi said. "We are going to win definitely and the political process would continue in Iraq."

Najaf police chief Ghalib al-Jazaari said that 50 people were arrested Monday in connection with the bombings. They included "elements" who had confessed to having links with the intelligence services of neighboring Syria and Iran, he claimed.

Iraq's Defense Minister Hazem Shaalan has accused both Iran and Syria of supporting terrorism in Iraq, although Allawi on Monday dismissed the allegations saying they did not reflect the government's position.

The deadly strikes on Sunday — against a funeral procession in Najaf and at a packed bus station in Karbala — once again highlighted the capability of the guerrillas to inflict massive casualties.

They also have undermined confidence in repeated claims by U.S. military commanders that their successful campaign last month to retake the town of Fallujah had dealt a serious blow to the rebellion.

Meanwhile, the head of Iraq's national electoral commission appealed to security forces to safeguard his officials after three of them were shot to death in a particularly audacious attack Sunday by dozens of guerrillas operating openly on the Haifa street in the heart of Baghdad. The ambush was the latest attack to target Iraqi officials working to organize the vote.

"We send an appeal to the Iraqi government and all the people to protect our employees," Abdul Hussein Al-Hindawi said. "We have no real protection because we work everywhere in the country and have more than 6,000 employees."

Allawi acknowledged Monday that the Haifa street ambush is a result "of the dismantling of the security forces in Iraq."

"What is happening is that we are facing an enemy heavily supported even in some cases with superior weapons," Allawi said. "We will have setbacks, we are having setbacks, but we are determined to continue the fight."

The security forces were nowhere to be seen while the armed gunmen conducted spot checks of cars and their occupants on Baghdad's main thoroughfare. It was only after the rebels had melted away following the execution of the election workers that U.S. Apache helicopters made a belated appearance over the site.

Insurgents also have been ramping up attacks against Iraq's interim administration — whose members they regard as traitors and American puppets — and its security forces.

There have been fears that the intimidation campaign against electoral workers will not only impact negatively on preparations for the ballot, but also could reduce turnout among voters on polling day to the point that it would undercut the legitimacy of the entire electoral process.

Observers say that preparations for the vote six weeks away have barely gotten underway in the country's central provinces.

As thousands of mourners attended funerals in Najaf on Monday, police there banned cars from entering the downtown area that houses the Imam Ali shrine to prevent future bombings, Gov. Adnan al-Zurufi said Monday.

Police chief al-Jezzairi said that among the 50 arrested suspects were people with links to Iran and Iraq.

"The police arrested some elements who confessed that they have links with the Syrian intelligence ... and a person who confessed he had links with Iranian intelligence since 1995," al-Jazaari said.

Also Monday, a roadside bomb planted near Baghdad's airport destroyed a U.S. Army Humvee, the military said. One of the soldiers was wounded.

Three more soldiers were wounded when a 1st Infantry Division patrol was ambushed near Balad, a town north of Baghdad, a U.S. military statement said. The casualties were in stable condition.

In the town of Ramadi, west of Baghdad, insurgents attacked a U.S. patrol with rocket-propelled grenades and machine guns in the center of the city, witnesses said. It was unclear whether there were any casualties in the clash.