BAGHDAD (Reuters) - A car bomb killed 25 people in mainly Shiite east Baghdad on Wednesday, a week after the bombing of a major Shiite shrine sparked sectarian bloodletting that has brought Iraq to the brink of civil war.

Police said the bomb, planted near a police checkpoint in the New Baghdad area, also wounded 58 people, mostly civilians. Another car bomb killed two people near a central bus station. A similar blast near a Sunni mosque caused no casualties.

The attacks occurred as Saddam Hussein admitted in court razing the farms of Shiites executed for involvement in an attempt on his life in the town of Dujail in 1982 but justified it as a legitimate punishment. "Where is the crime?" he asked.

The former leader's trial is overshadowed by fears Iraq's sectarian tensions are out of control after reprisal killings that officials say have cost more than 450 lives.

The toll could be much higher as many people say relatives have just disappeared. Saddam, a Sunni who justified his harsh rule by the need for national unity, took the chance to comment from the dock, though in more measured tones than earlier in the trial. "The people must be united," he said.

"All religions, all ethnic groups."

"God willing, we shall be," replied the chief judge, a Kurd who has been strict with the eight defendants but gave Saddam time to say his piece, ensuring nationwide television coverage.

Prosecutors presented documents and other evidence they said showed that Saddam ordered 148 Dujail men executed after a mere show trial. His case was adjourned again until March 12.

Religious representatives of the once-dominant Sunni Muslim minority, accusing the Shiite-led government and U.S. forces of failing to halt attacks by Shiite militiamen, called on Sunnis to come out in force to protect their mosques.

Saddam-era tanks from the new, U.S.-trained Iraqi army have deployed to protect some threatened neighborhoods and the U.S. military says it has a rapid reaction force standing by.

Shiite Prime Minister Ibrahim al-Jaafari said he would move ahead rapidly to form a national unity government Washington has been pressing for since Sunnis took part in a December election.

But signs of opposition to Jaafari's appointment as prime minister emerged. Political sources said Kurdish, Sunni and secular leaders discussed whether to work with Jaafari, who last month won an internal ballot in the dominant Shiite Islamist Alliance by a single vote against stiff opposition.

The main Sunni bloc has boycotted negotiations in protest at the violence and a senior Shiite government official said on Tuesday it would take at least two months to forge a coalition, raising questions over how effectively the authorities can tackle Iraq's gravest crisis since the U.S. invasion of 2003.

In some districts, residents have formed armed patrols and thrown up barricades. Sunnis fear Shiite militias nominally loyal to parties in the U.S.-backed interim government, while Shiites worry about Sunni insurgents whose past attacks have targeted Shiite civilians as often as U.S. or Iraqi forces.

Families have fled their homes in some areas. Others say they are packed and ready to run if need be.

On Tuesday, when bombs killed some 60 people in Baghdad, U.S. President George W. Bush said Iraqis faced a choice between "chaos or unity". But, with polls showing his popularity dropping among Americans, he dismissed talk of civil war.

Any full-scale civil war could inflame the entire Middle East and thwart Bush's hopes of withdrawing U.S. troops.