At least 24 people were killed Monday by bombings across Iraq, including a homicide attack on a bus in Baghdad that left 12 dead.

The U.S. command said an American soldier was killed by a roadside bomb southeast of Karbala, about 50 miles southeast of Baghdad. The soldier's name was not released pending notification of kin.

In Baghdad, a homicide bomber detonated an explosives belt on a bus in the Shiite district of Kazamiyah, killing 12 people and injuring 15, police said. Earlier, a bomb exploded next to tea stalls near Liberation Square, killing at least four day laborers and wounding 14, police said.

In Mosul, 225 miles northwest of Baghdad, a homicide attacker blew himself up in a restaurant packed with policemen eating breakfast, killing at least five people and wounding 21, including 10 policemen, officials said.

Two more civilians died when a car bomb exploded in Madain southeast of Baghdad, police said. Eleven people, including three women, were injured.

As the violence rages, the country faces a political deadlock, which prompted the U.S. ambassador to warn Iraqi politicians they risk a loss of American support if they do not establish a genuine national unity government.

U.S. Ambassador Zalmay Khalilzad delivered his blunt warning during a rare press conference after signs that talks on a new government following the December elections were not going well because of sharp differences among the country's Shiite, Sunni Arab and Kurdish political parties.

Failure to establish a unity government that includes a strong role for Sunni Arabs would fail to undermine the Sunni-dominated insurgency and throw into question U.S. plans for a phased withdrawal of the 138,000 American troops here.

Khalilzad said that overcoming the sectarian and ethnic divide requires a government of national unity, which is "the difference between what exists now and the next government." The outgoing government is dominated by Shiites and Kurds.

Khalilzad told the Shiites that the key security Defense and Interior ministries must be in the hands of people "who are nonsectarian, broadly acceptable and who are not tied to militias."

The ambassador reminded the Iraqis that the United States has spent billions to build up Iraq's police and army and "we are not going to invest the resources of the American people and build forces that are run by people who are sectarian."

Sunni Arabs accuse the Shiite-led Interior Ministry of human rights abuses and using Shiite militias against Sunni civilians under the cover of fighting the insurgency. Shiites deny the charge and say they must control security forces to protect Shiites against attacks by Sunni religious extremists.

Khalilzad cited the need for compromise, especially in the Defense and Interior ministries. He said ministers in those posts must be those "who are nonsectarian, broadly accepted and who are not tied to militias."

Otherwise, he warned that "Iraq faces the risk of warlordism that Afghanistan went through for a period." Khalilzad was born in Afghanistan and served as U.S. envoy there.

Several Shiite parties are believed to control armed militias, some of which date back to the Iran-Iraq war of the 1980s when many Iraqi Shiites fled to Shiite-dominated Iran. On the other hand, most of the insurgents are Sunnis. Kurds maintain the biggest armed force — the peshmerga — which they maintain is the legitimate security force of their autonomous government in the north.

Shiites and Kurds dominate the ranks of the Iraqi army and police, although the United States is stepping up efforts to recruit Sunnis into those institutions.

A coalition of Shiite religious parties won 130 of the 275 seats in the new parliament. Although they have agreed in principle to a unity government, Shiite leaders insist their showing in the Dec. 15 election gives them the democratic right to control key levers of the new government.

A Kurdish alliance won 53 seats and two Sunni Arab blocs together took 55 seats — a major increase over Sunni representation in the outgoing parliament.

Iraqis have until mid-May to form a new government, but U.S. and Iraqi officials warn the process could take longer because of political differences.

Control of the security ministries is only one of several major differences standing in the way of a political agreement. Shiites insist that Sunni Arab parties work actively against the insurgency. Sunnis insist on drawing a difference between "legitimate resistance" to foreign occupation and terrorism that targets civilians.

Shiites, who comprise about 60 percent of the population, are reluctant to surrender power won at the ballot box to Sunni Arabs, who dominated political life here during Saddam Hussein's regime. Sunni Arabs insist that programs to purge Saddam's supporters from public life be limited and not used to deprive Sunnis of a future in Iraq.

Kurds zealously guard the self-rule they have enjoyed since 1991, and many of them want to expand their autonomous region to oil centers around Kirkuk, claimed by Kurds, Arabs and Turkomen.

Also Monday, a British official said two Macedonian contractors were freed by kidnappers four days after they were abducted in Basra.

The freed Macedonians worked for the Ecolog cleaning company at Basra International Airport and were abducted Thursday. Their kidnappers had demanded a $1 million ransom from their employers, but it was unclear if any money had been paid.

The British official, who spoke on condition of anonymity because he was not authorized to speak to the media, confirmed their release.

More than 250 foreigners have been kidnapped in Iraq, including American reporter Jill Carroll, who was abducted Jan. 7 in Baghdad. At least 39 have been killed.