BAGHDAD, Iraq – Iraq’s transition to democratic self-rule received two huge blows on Wednesday: a massive car bombing that killed 68 Iraqis and the decision by a major Sunni political party to pull out of an important national political conference scheduled for Saturday.

In Baqouba, about 22 miles northeast of Baghdad, a devastating explosion triggered by a suicide car bomber near a crowd of prospective police recruits killed at least 68 people and injured 56, Iraqi officials said.

The death toll was the largest for any suicide bombing since the June 28 handover of sovereignty and one of the largest for such an attack since the war started.

In Baghdad, a large, moderate-to-conservative Sunni Muslim political party announced Wednesday that it was withdrawing from a national political conference, set to start Saturday. The Iraqi National Conference is part of the U.N.-backed process to chart Iraq’s political future and choose a 100-member interim national assembly before parliamentary elections by early next year.

Iraqi Islamic Party leader Muhsen Abdul Hamid, a member of the disbanded governing council that preceded the current interim government, said voting violations – including violence and forgery – in regional caucuses to elect conference delegates spurred the party’s withdrawal.

Organizers have acknowledged serious problems in the delegate selection process and have even stepped in to nullify the results of some caucuses.

The withdrawal threatens to undermine the credibility of the democratic transition by leaving out a major player. Iraq’s Sunni Muslim minority occupied a privileged position under Saddam Hussein’s regime and they are believed to be behind many of the attacks on U.S. and Iraqi security forces. Their continued alienation from the political process threatens to block a possible successful outcome.

The Baqouba blast, which occurred around 10:15 a.m. along a busy thoroughfare, tore into a dense gathering of at least 300 would-be policemen, as well as people in nearby shops and on sidewalks, according to Iraqi officials and witnesses. Most of the dead were prospective police recruits, but the fatalities also included all 21 occupants of a passing minibus.

In the bombing’s aftermath, charred corpses lay on the street amid pools of blood. Shrapnel littered the ground for several hundred yards. Ambulances and police pickups raced back and forth from the site to the hospital, ferrying the dead and wounded.

“I saw many bodies lying on the street,” said police Lt. Majid Hussein, 20. “I saw many pieces of human bodies. I saw heads and hands.”

Also Wednesday, military officials reported that one U.S. soldier was killed and three injured in an improvised explosive device attack on a patrol in Balad Ruz, about 50 miles northeast of Baghdad around 8:15 p.m. Tuesday. The soldiers’ names weren’t released.

In Suwayrah, about 50 miles south of Baghdad, approximately 35 insurgents were killed in a 7 a.m. battle Wednesday with Iraqi and multinational forces, including U.S. troops, military officials said. Seven members of Iraqi forces died and 10 were injured.

In central Baghdad, a rocket on Haifa Street attack killed two Iraqi civilians Wednesday. The street has been the scene of at least two attacks on Iraqi or American forces in recent weeks.

Interior Ministry spokesman Sabah Kadhim called the Baqouba bombing a “deplorable act” that “has no logic by any religion of the world.”

He said the government had no information about who, if anyone, had claimed responsibility for the attack. “It only needs one man with a lot of explosives to do it. When you think about it, it’s not as though it’s a major operation by a lot of people. Iraq is awash with weapons.”

The attack was the latest targeting Iraq’s police or national guard. Insurgents view them as collaborators with American and other foreign troops.

The car bomb exploded near a police building where prospective recruits, mostly former Iraqi army officers, had been lining up to apply for the force or learn the status of their applications.

The crowd of men had gathered in the relative safety of an alley. They moved into the main street, expecting to be allowed in the police building as a police official began calling out the names of men who had been recruited, witnesses said.

Instead, police kept all or most of the men outside, next to the building and a row of small shops. At that point, the suicide bomber drove a black sedan toward the crowd before detonating the explosives.

A nearby grocer said 300 to 400 prospective recruits were gathered at the time. An injured prospective recruit said the crowd could have been as large as 700.

“When we moved to get inside the police station, they told us to get back,” said recruit Ahmed Jassim, 26, from his bed at Diyala General Hospital in Baqouba as he waited for doctors to treat his broken leg. “When we left the car bomb came.”

Wounded men filled the hospital’s two floors of wards and spilled into stairwells. Frantic relatives dashed around seeking loved ones or sat anxiously at their bedsides.

There were no reports of Iraqi police or other security forces killed or injured in the blast. High concrete barriers spared the police building from major damage, but the blast demolished at least six cars on the street and the facades of at least six adjacent shops.

“This is a very sad thing, because those people (killed) are innocent,” said Luay Khalif, 35, whose snack shop was badly damaged by the explosion. “Islam will never agree with such things.”

Baqouba has been the site of frequent attacks against Iraqi or foreign forces. The town of mostly Sunni Muslim residents is part of the so-called Sunni Triangle, a hotbed of resistance.

Kadhim, the Interior Ministry spokesman, said Wednesday’s brutal body count wouldn’t change Iraq’s course.

“They’re just trying to weaken the government, but our resolve is more than doubled,” Kadhim said. “We have no option but to fight these people to the end.”