BAGHDAD - The bloodiest day of the year in Iraq left at least 69 people dead in a series of bombings in mainly Shiite areas Friday - concerted attacks seen as demonstrating the resilience of the Sunni-led insurgency after the slaying of two al-Qaida leaders last weekend.

No one has taken responsibility for the blasts, but officials were quick to blame Sunni-led insurgent groups for attacking at a particularly fragile time as Iraq awaits formation of a new government and prepares for U.S. troops to go home by the end of next year.

The protracted political wrangling since contentious March 7 elections has raised fears of sectarian violence akin to that seen at the height of the war.

Prime Minister Nouri al-Maliki lashed out at the bombers in a statement Friday night, saying the insurgents were trying to fight back after Iraqi security forces killed the two al-Qaida in Iraq leaders on April 18.

"The cowardly terrorist attacks that occurred today were intending to cover the great success achieved by the security forces through the killing of the leaders of wickedness and terrorism, Abu Omar al-Baghdadi and Abu Ayyub al-Masri," al-Maliki said.

He also called on Iraqis to stand firm against Baathists, former members of the Baath Party that ruled Iraq under Saddam Hussein. The term "Baathist" strikes a particular chord with many Shiites who fear the party's followers may yet rise again to rule the country; Sunnis often feel the word is a thinly veiled attack on all of the minority sect.

Officials have warned that the insurgents remain capable of staging high-profile bombings despite the killing of their two leaders, which U.S. Vice President Joe Biden called a "potentially devastating blow" to al-Qaida in Iraq.

Friday's apparently coordinated attacks came in a two-hour span shortly after the Shiites' call to prayer across the capital. The major blasts were in former Shiite militia strongholds, underscoring the insurgents' professed aim of provoking a new round of sectarian bloodshed. Among the targets of the car and roadside bombs were three Shiite mosques.

In the vast eastern Baghdad slum of Sadr City, hundreds of worshippers knelt on prayer mats in the streets surrounding the offices of anti-U.S. cleric Muqtada al-Sadr when the deadliest blasts went off.

Four strategically located car bombs timed to maximize the carnage killed at least 36 people and wounded nearly 200, according to hospital and police officials who spoke on condition of anonymity because they were not authorized to talk to the media.

Aqil Ibrahim, 35, was fixing his taxi when he heard the first explosion.

"I went to see what was going on and to help the wounded worshippers. I saw pieces of human flesh on the ground," he said, holding his bandaged hand.

Flames shot out of nearby parked cars and motorcycles. Blood mixed with water streamed down muddy streets as firefighters worked to put out the blazes, and passers-by frantically tried to help. Shouting men loaded the wounded onto trucks to rush them to the hospital.

One man ran carrying a young girl in a bloodstained pink dress. Others could be seen picking up human remains and burying them in a nearby field before sunset in accordance with Islamic law.

Onlookers in Sadr City threw stones at arriving Iraqi security forces, frustrated that the troops cannot secure the city. The troops fired their guns in the air to scatter the crowd.

Two of the bombs exploded in the mainly Shiite neighborhood of Zafaraniyah, killing one person and wounding 12.

Two others targeted mosques linked with prominent Shiite political leaders. A car bomb at the Hadi al-Chalabi mosque in the Hurriyah neighborhood killed eight people and wounded 19. The mosque is named after the father of Ahmed Chalabi, who was behind much of the faulty intelligence that resulted in the U.S.-led invasion and has since led efforts to bar many Sunni political figures from office.

A bomb targeting the Muhsin al-Hakim mosque killed 14 people and wounded 36. That mosque is named after the grandfather of Ammar al-Hakim, a leading Shiite political figure whose party has ties to Iran.