In all, at least 68 people were killed or found dead nationwide Monday, police said. They included the bullet-riddled bodies of 30 men found in Baghdad ¡ª the apparent victims of sectarian death squads.

All but two were found in west Baghdad, including 17 in the Amil neighborhood where Sunni politicians have complained of renewed attacks by Shiite militiamen, said a police official who spoke on condition of anonymity because he was not supposed to release those details.

Sunni complaints prompted the country's Sunni vice president to threaten to leave the Shiite-dominated government unless key unspecified amendments to the constitution are not made by May 15.

The power struggle among the Sunnis, which surfaced last year, could prove decisive in the U.S. campaign to win over significant portions of the Sunni community, which has formed the bedrock of the insurgency.

The first of the Ramadi area attacks happened about noon in a market on the northwest outskirts of the city, killing eight people and wounding 13, said police Col. Tariq Youssef.

About 15 minutes later, police at a nearby checkpoint spotted a second car bomb and opened fire, but the driver was able to detonate the vehicle, Youssef said. Five people, including two policemen, were killed and 12 were wounded, Youssef said.

The attacks occurred in areas controlled by the Anbar Salvation Council, an alliance of Sunni tribes formed last year to drive al-Qaida from the area. Council officials blamed the attacks on al-Qaida.

"They committed this crime because we have identified their hideouts and we are chasing them," said Sheik Jabbar Naif al-Dulaimi.

In a Web statement Monday, an al-Qaida front organization, the Islamic State of Iraq, warned Sunnis against joining the government security forces ¡ª a move supported by the Salvation Council.

"We tell every father, mother, wife or brother who does not want to lose a relative to advise them not to approach the apostates and we swear to God that we will use every possible means to strike at the infidels and the renegades," the group said.

The Islamic State also claimed responsibility Monday for attacks that killed 34 people over the weekend ¡ª including six U.S. soldiers and a Russian embedded photojournalist who died in a roadside bombing in Baqouba.

The 34 also included the police chief of Samarra, Col. Jalil Nahi Hassoun, who was killed Sunday in an attack on police headquarters. He was buried Monday following a tearful procession by police in blue uniforms who escorted the flag-draped coffin as it was driven in the bed of a white pickup truck through the Sunni city.

At least five al-Qaida fighters were killed in the fighting in Samarra, a U.S. military official told The Associated Press, speaking on condition of anonymity because he was not authorized to release details of the attack.

Also Monday, the military announced a U.S. soldier was killed by small-arms fire in western Baghdad the day before, bringing to nine the number of American personnel slain Sunday.

The security situation in the capital figured high in talks between Prime Minister Nouri al-Maliki and President Bush, who conferred Monday in a video conference.

Al-Maliki told Bush of the need to maintain cooperation between U.S. and Iraqi forces as they continue their campaign to end the chaos and violence in Baghdad, the prime minister's office said in a statement.

White House spokesman Tony Snow said Bush and al-Maliki spoke about the Iraqi leader's push for political reconciliation, which is considered vital to bring stability.

The two leaders spoke for about 25 minutes with staff members in attendance, then for another period of time one-on-one, Snow said.

"The prime minister is working with the presidency council to advance the political process in Iraq, including a lot of the legislation that we've been discussing over the last few months," Snow told reporters. "But issues of communications and reconciliation were at the fore."

Al-Maliki, a Shiite, reiterated his determination to work with Sunni leaders, Snow said.

But al-Maliki's government remains burdened by "narrow agendas" standing in the way of unity and crucial U.S.-backed legislation, such as a proposed law to share Iraq's oil wealth, said Gen. David Petraeus, the top U.S. commander in Iraq. Petraeus spoke Monday to the annual meeting of The Associated Press.

In an interview with CNN, Iraqi Vice President Tariq al-Hashemi said he would lead a Sunni walkout from the Cabinet and parliament if changes are not made to the constitution by May 15. He also said he turned down an offer by Bush to visit Washington until he can count more fully on U.S. help, CNN said on its Web site.

A walkout by the Sunnis, who control 44 of the 275 parliament seats and five Cabinet posts, would plunge Iraq into a political crisis.

The international Red Cross announced Monday it would increase its operations to provide food, water and medical treatment for hundreds of thousands of Iraqis who have fled their homes but remain in the country.

"This conflict is inflicting immense suffering on all Iraqis," Beatrice Megevand-Roggo, head of the organization's Middle East operations, said in Geneva. "Civilians are bearing the brunt of the relentless violence."

Hundreds of thousands of other Iraqis have fled to Jordan and Syria.

Jordan said Monday that the more than 750,000 displaced Iraqis residing in the country has cost the government $1 billion a year and increased Jordan's population by 14 percent.

Late Monday, the Islamic State of Iraq said it had captured five Iraqi army officers and four policemen in Diyala province and threatened to kill them unless authorities freed Sunni women held in Iraqi prisons and turned over "all those who killed our people" in the northern city of Tal Afar.

No deadline was given. There was no way to check the authenticity of the claim, which appeared on an Islamic extremist Web site and included pictures of nine men, all in uniform and facing the camera.