Updated

A car bomb exploded Sunday near the gate to a U.S.-run base north of Baghdad (search), killing six people and injuring 20 others — including two U.S. soldiers, the U.S. military said. It was the latest of a series of attacks against occupation forces and their Iraqi allies.

Gunmen blasted a police station in Baghdad's Shiite neighborhood Sadr City (search) on Sunday, rigging the building with explosives after Iraqi police departed. Late Saturday, a police station south of the capital also was blown up and seven policemen killed.

The attacks raise questions about the capability of local security forces to control public order after sovereignty passes to the Iraqis at the end of this month.

Also Sunday, the U.S. military freed more detainees from the notorious Abu Ghraib prison (search), the center of the scandal involving abuse of inmates by American soldiers. The release was the fourth major one from the facility since the scandal broke in April.

Some of the 320 detainees released Sunday complained they were forced to eat food fit only for animals, though they said the quality had improved in recent weeks.

Elsewhere, seven Iraqi policemen were killed in an attack on a police station south of Baghdad, officials said Sunday. The police station was blown up in the raid.

Ambulances, Humvees and Iraqi police rushed to evacuate the injured at the Taji air base, 12 miles (20 kilometers) north of Baghdad. U.S. soldiers cleared the area at the former Iraqi air force base now used by the U.S. Army's 1st Cavalry Division.

In another attack Sunday, a roadside bomb exploded as a U.S. convoy passed in the Baghdad Shiite neighborhood of Sadr City, killing a 14-year-old boy and injuring two Iraqi police officers, Iraqi police said. There were no reports of American soldiers wounded.

Iraq's new prime minister, Iyad Allawi (search), has called for a halt to attacks on Americans and other foreign soldiers, saying their presence would be needed even after the transfer of sovereignty to help the new leadership improve security.

Despite the attacks, tensions have eased in the Shiite holy cities of Najaf and Kufa after a deal enabling Iraqi police to extend their control from gunmen loyal to radical cleric Muqtada al-Sadr. U.S. troops who have been fighting the militia have agreed to allow the police to take over security, thus reducing the chances of clashes.

Saturday's roadside bombing, which occurred in eastern Baghdad, was the second fatal attack against American troops in the capital in as many days. Five U.S. soldiers were killed and five wounded Friday in an ambush near the Shiite neighborhood Sadr City, an al-Sadr stronghold.

Assailants also ambushed two civilian sport utility vehicles on the road to Baghdad's international airport on Saturday, killing two Americans and two Poles working for Blackwater USA, Poland's top diplomat in Baghdad said. Charge d'affaires Tomasz Gielzecki, told The Associated Press that another Pole was also injured in the attack, but gave no other details.

Four other civilian security personnel from Blackwater, a North Carolina-based company were killed March 31 after their vehicle was hit by rocket-propelled grenades in Fallujah. That prompted a three-week Marine siege of Fallujah that left 10 Marines and hundreds of Iraqis dead — but ended with the Blackwater killers still at large.

Another civilian car carrying Westerners was attacked Saturday in the northern city of Mosul. Police said one civilian was killed and three others were injured but they refused to identify them by nationality.

Late Saturday, eight people disguised as police stormed a police station in Musayyib, 70 kilometers (45 miles) south of Baghdad, killed seven officers and then blew up the building.

Late Saturday, residents reported an armed clash in Fallujah, the restive Sunni Muslim city that was the scene of heavy fighting between Marines and insurgents last April. However, a coalition spokesman said no U.S. personnel were involved in any action in the city, where security is in the hands of an Iraqi unit organized with U.S. support after the Marines lifted their siege in late April.

With tensions easing in Najaf, al-Sadr met late Saturday with Iraq's most influential spiritual leader, Grand Ayatollah Ali al-Husseini al-Sistani, for the first time since the young cleric launched an uprising against the U.S.-led coalition in April.

Al-Sistani thanked al-Sadr for his moves to resolve the crisis, according to an al-Sadr aide, Ahmed al-Shibani. "The agreement is moving is toward success and is on the right path," al-Shibani said.

Al-Sadr's rebellion began after the U.S.-led occupation authority closed his newspaper, arrested a key aide and announced a warrant for his arrest in the April 2003 murder of a moderate cleric in Najaf.

Under a deal worked out between Shiite leaders and al-Sadr's militia, his al-Mahdi Army is supposed to pull back from the Islamic shrines in the twin cities and hand over security to Iraqi police.

The U.S. Army acceded to a request from the local governor to keep U.S. troops away from the Imam Ali Shrine in Najaf and the mosque in Kufa where al-Sadr preaches to give Iraqi security forces a chance to ease tensions.