BAGHDAD, Iraq -- Revenge-seeking Shiite militiamen seized six Sunnis as they left Friday prayers, drenched them with kerosene and burned them alive, and Iraqi soldiers did nothing to stop the attack, police and witnesses said.

The fiery slayings in the mainly Sunni neighborhood of Hurriyah were a dramatic escalation of the brutality coursing through the Iraqi capital, coming a day after suspected Sunni insurgents killed 215 people in Baghdad's main Shiite district with a combination of bombs and mortars.

The attacks culminated Baghdad's deadliest week of sectarian fighting since the war began more than three years ago.

Police Capt. Jamil Hussein said Iraqi soldiers at a nearby army post failed to intervene in the burnings of Sunnis carried out by suspected members of the Shiite Mahdi Army militia, or in subsequent attacks that torched four Sunni mosques and killed at least 19 other Sunnis, including women and children, in the same northwest Baghdad area.

Imad al-Hasimi, a Sunni elder in Hurriyah, confirmed Hussein's account. He told Al-Arabiya television he saw people who were soaked in kerosene, then set afire, burning before his eyes.

Two workers at Kazamiyah Hospital said the bodies from the clashes and immolations had been taken to the morgue at their facility. They refused to be identified by name, saying they feared retribution.

In spite of the police and witness accounts, however, President Jamal Talabani appeared to discount the reports. He emerged from meetings with other Iraqi political leaders late Friday and said Defense Minister Abdul-Qader al-Obaidi told him that the Hurriyah neighborhood had been quiet throughout the day.

According to Hussein, the police official, militiamen rampaged through the district, setting fire to several homes in addition to the four mosques that were bombed and burned.

Some residents claimed that the Mahdi Army, the militia loyal to radical anti-American Shiite cleric Muqtada al-Sadr, has begun kidnapping and holding Sunni hostages in order to slaughter them at funerals of Shiite victims of Baghdad's sectarian violence.

Such claims cannot be verified but speak to the deep fear that grips Baghdad, where retaliation has become a part of daily life.

In the past year, thousands of bodies have been found dumped across Baghdad and other cities in central Iraq, victims who were tortured, then shot to death, according to police. The suspected militia killers often have used electric drills on their captives' bodies before killing them. The bodies are frequently decapitated.

Burning victims alive, however, introduced a new method of brutality that seemed likely to be reciprocated by the other sect as the Shiites and Sunnis continue killing one another in unprecedented numbers. The attack, which came despite a curfew in Baghdad, capped a day in which at least 87 people were killed or found dead in sectarian violence across Iraq.

The Association of Muslim Scholars, the most influential Sunni organization in Iraq, said even more Sunni victims were killed. It claimed a total of 18 people had died in an inferno at the al-Muhaimin mosque.

The extreme violence continued to tear at the Iraq's social fabric even after the government had banned pedestrians and cars from the streets and closed the international airport until further notice in anticipation of a storm of retaliation for the five bombings and two mortar rounds that killed 215 in Sadr City on Thursday.

The airport closure forced Talabani to delay his planned Saturday departure for Tehran for meetings with President Mahmoud Ahmadinejad. The Iranian leader also invited Syrian President Bashar Assad, but it now appeared he would not attend.

The chaos also cast a shadow over the Amman, Jordan, summit next week between Prime Minister Nouri al-Maliki and President Bush.

Politicians loyal to al-Sadr threatened to boycott parliament and the Cabinet if al-Maliki went ahead with the meeting. The radical Shiite political bloc, known as Sadrists, is a mainstay of support for al-Maliki, himself a Shiite. The Mahdi Army is the organization's armed wing.

Sadrist lawmaker Qusai Abdul-Wahab blamed U.S. forces for Thursday's attack in Sadr City because they failed to provide security.

"We say occupation forces are fully responsible for these acts, and we call for the withdrawal of occupation forces or setting a timetable for their withdrawal," Abdul-Wahab said.

A U.S. helicopter patrolling above Sadr City came under intense fire from the ground and shot back, wounding two people Friday night, according to police 1st. Lt. Qassim Mohammed and witnesses.

The U.S. military said the helicopter had taken fire from six rockets launched from one site and destroyed the launcher. The military statement did not address whether there were casualties.

White House spokesman Scott Stanzil said the president's plans to meet with al-Maliki on Wednesday and Thursday were unchanged.

Al-Maliki is increasingly at odds with the Bush administration for his refusal to disband militias and associated deaths squads that are believed responsible for killing thousands of Sunnis since an al-Qaida attack blew up the golden dome of a revered Shiite shrine on Feb. 22 in Samarra, north of Baghdad.

Mortar fire rained down again on Sunni Islam's holiest shrine in Baghdad, the Abu Hanifa mosque in the Azamiyah neighborhood, wounding at least five people. Several mortars crashed into the area Thursday night within hours of the attacks in Sadr City, one of them puncturing the dome of the shrine and damaging the interior, including its library.

Also, militia gunmen raided a Sunni mosque in the Amil section of west Baghdad, killing two guards, police 1st Lt. Maitham Abdul-Razzaq said.

And in Baqouba, 35 miles northeast of Baghdad, Sunni insurgents blew up the dome of the important Shiite mosque of leading cleric Abdul-Karm al-Madani.

In the northern Iraqi city of Tal Afar, 23 people were killed and 43 wounded when explosives hidden in a parked car and in a suicide belt worn by a pedestrian detonated simultaneously outside a car dealership, said police Brig. Khalaf al-Jubouri.

Altogether, 56 people were killed across in Iraq on Friday, and police said they found 31 bodies dumped throughout Baghdad, most of them tortured before being shot.

In Sadr City, cleanup crews continued removing remains of the dead from wreckage of the car bombs, and tents were erected throughout the ramshackle district for relatives to receive condolences.

Hundreds of men, women and children beat their chests, chanted and cried as they walked beside vehicles carrying the caskets of their loved ones toward the holy Shiite city of Najaf for burial. Despite Baghdad's curfew, al-Maliki, himself a Shiite, ordered police to guard the processions.

As the funeral processions reached the edge of Sadr City in northeastern Baghdad, the cars and minivans left most of the mourners behind and began the 100-mile drive south to Najaf, a treacherous journey that passes through many checkpoints and areas controlled by Sunni militants in Iraq's so-called "Triangle of Death."

AP correspondents Thomas Wagner, Bassem Mroue and Qais al-Bashir contributed to this report.