Blood and shrapnel covered the grounds of the ancient Kufa (search) mosque compound Thursday after at least two mortar blasts ripped through a crowd of Iraqis gathered to march to the holy city of Najaf (search), killing at least 27 people and wounding at least 63.

The explosions tore chunks from the walls of the Kufa mosque, a revered Shiite site dating to the earliest days of Islam. Television footage showed bloodied survivors heaving corpses onto truck beds.

The mosque violence was the fourth attack in two days around Kufa; the other three killed marchers and bystanders at rallies. At least 40 people total have been killed and 165 wounded in the recent bloodshed, and as night fell, it remained unclear who was responsible.

The mortar shells whistled overhead and hit the mosque grounds Thursday morning as the building and its yard were packed with people heeding a call from Grand Ayatollah Ali Husseini al-Sistani (search) to join him in bringing peace to neighboring Najaf.

The Kufa mosque is the usual pulpit for radical cleric Muqtada al-Sadr, whose militia has been holed up for weeks in a Najaf shrine battling U.S. and Iraqi forces and whom al-Sistani approached Thursday with a cease-fire plan.

After the blasts, the morgue at the nearby hospital overflowed with casualties. At least 15 bodies covered with plastic sheets lay in a garden outside, with mourners huddled around them.

One man, his robe stained with blood, shivered with sobs as he sat next to a body. "Mohammed! Mohammed," he cried, beating his chest.

Inside the hospital, distraught people ran through the corridors or fanned the wounded with towels. The injured cried out in pain.

"May God damn America," another man yelled. He held a pint of IV fluid for an injured companion.

Those at the scene blamed the U.S.-allied Iraqi military or Americans for the blasts -- charges both denied. Allawi blamed an unspecified "spiteful group" opposed to peace.

A U.S. military official said it was possible guerrillas firing at nearby Iraqi National Guard positions overshot their target and hit the mosque. The official said the blasts also could have been caused by misfiring rebel munitions.

"This is savagery," said Hameed Jassim, a worshipper from nearby Kut who was injured in the leg. "There were thousands of us outside when the explosion took place."

The mosque attack came a day after another unexplained blast in Kufa, apparently also caused by a stray mortar shell. It killed two civilians, one an 8-year-old boy.

In violence later Thursday, others heeding al-Sistani's call filled the road into Najaf, strolling unarmed but carrying shimmering green-and-red Shiite flags. As they passed an Iraqi National Guard base, gunmen peppered the procession with automatic weapons fire, witnesses said. At least three people were killed and 46 wounded.

It was unclear who attacked. A witness said there were scruffy, armed men belonging to al-Sadr's militia blocking a street to make room for the marchers when the shooting broke out.

As the firing began, panicked marchers turned and ran back toward Kufa, barreling into the crowd behind them.

A day earlier, another procession to Najaf was ambushed at the same spot. Associated Press Television News footage showed demonstrators first chanting slogans in favor of al-Sadr and against the Iraqi prime minister, then fleeing in panic under a flurry of bullets.

Hospital officials said eight people were killed and 56 wounded. APTN footage showed furious participants displaying bloodied wounds. The men shouted that they were not part of al-Sadr's militia.

Witnesses said the gunfire appeared to come from the National Guard post, which sat behind concrete blast walls along the parade route. But an Interior Ministry official said there was no reason for Iraqi police or National Guard to target peaceful processions, suggesting foreign fighters shot the marchers in a bid to sow chaos.