BAGHDAD, Iraq — U.S. forces aggravated sectarian tensions in Iraq yesterday by mistakenly arresting a prominent Sunni Muslim leader.

Suicide bombers, meanwhile, killed at least 27 people in a southern town and four U.S. Air Force personnel and an Iraqi were killed in the crash of an Iraqi aircraft.

Mohsen Abdul-Hamid, head of the Iraqi Islamic Party, was detained when U.S. troops raided his home shortly before dawn. He was released after Iraqi government officials, including Prime Minister Ibrahim al-Jaafari, criticized the action.

Abdul-Hamid had been a voice of reconciliation, urging Sunnis to work with the Shiite-dominated government and condemning a surge in sectarian killings.

A statement released by U.S.-led forces said the raid, which left Abdul-Hamid's house with battered doors and smashed windows, was a case of mistaken identity.

"Mr. Abdul-Hamid is being returned to his home," according to the statement. "Coalition forces regret any inconvenience and acknowledge Mr. Abdul-Hamid's cooperation in resolving this matter."

Speaking on Iraqi television, al-Jaafari called Abdul-Hamid a well-respected politician and noted that the detained leader had once served as president of the former Iraqi Governing Council. The Iraqi government worried that the embarrassing incident would deepen Sunni suspicions about the new government and its American backers.

"I will demand a clear accounting of this," said al-Jaafari, a Shiite Muslim whose administration has been negotiating with Sunni leaders to avert further sectarian violence. "What happened is wrong. ... No civilian should be arrested without just cause."

The arrest came on another bloody day in Iraq.

Men with explosives strapped to their bodies killed at least 27 people and wounded 118 when they detonated in the predominantly Shiite town of Hillah, about 60 miles south of Baghdad.

The first attacker slipped unnoticed into a gathering of police commandos, detonating explosives that tore through the crowd. As frenzied survivors dashed for the shelter of a nearby building, two other bombers ran with them before setting off simultaneous blasts, witnesses said.

The coordinated assault targeted police officers who were protesting a provincial governor's decision to disband their units.

Meanwhile, the crash of an Iraqi military aircraft that killed four U.S. Air Force personnel and an Iraqi, the only other person on board, occurred yesterday near the village of Jalula, about 80 miles northeast of Baghdad, U.S. military spokesman Lt. Col. Fred Wellman said today. It was unclear what type of aircraft it was, who was in control or why it crashed.

And on Memorial Day, the U.S. military said Spc. Phillip Sayles of the Army's 1st Battalion, 24th Infantry Regiment was killed in an attack Saturday in the northern city of Mosul. As of yesterday, at least 1,657 U.S. military personnel had died since the beginning of the Iraq war in March 2003, according to an Associated Press count.

In the greater Baghdad area, 40,000 Iraqi soldiers and police cordoned streets and swept through neighborhoods in the third day of an anti-insurgency operation. The sweeps, which have resulted in more than 500 arrests, are targeting insurgents in neighborhoods such as Abu Ghraib, where U.S. and Iraqi military officials say car bombs are manufactured and rebels find cover amid a sympathetic public.

Traffic was heavy around an estimated 675 checkpoints and gunfire echoed through the city, but Iraqi forces did not encounter the fierce resistance of Sunday, when about 50 insurgents attacked a roadblock in a firefight that left nine soldiers and 14 guerrillas dead. So far, more than 760 Iraqis have been killed in sectarian and insurgent violence that has permeated the country since the new government was named April 28.

"Getting control of a city of 5 million is not an easy proposition," said a senior U.S. official who asked not to be identified. "They're making some progress," he said, but the progress has been uneven.

The brief detention of the Sunni politician Abdul-Hamid by U.S. forces, which angered Iraqi officials including President Jalal Talabani, came as Shiite and Sunni leaders were attempting to ease distrust between religious groups. A minority population, the Sunnis controlled the country under Saddam Hussein's Baathist regime. Today, they make up the core of the insurgency.

Although Abdul-Hamid had been a member of the Iraqi Governing Council, the now-dissolved U.S.-backed government formed after the war, he had grown disenchanted by what he viewed as discrimination and bloodshed against Sunnis. His moderate Iraqi Islamic Party refused to take part in national elections in January that resulted in a government controlled by Shiites and Kurds.

In an interview shortly before the election, Abdul-Hamid vowed that Sunnis would "not recognize the legitimacy of this election, and they will not follow its decisions or laws."

But as sectarian tensions widened in recent weeks, Abdul-Hamid called for Sunnis to join the political process in order to avoid a civil war. His tone was more conciliatory than the radical message of the Muslim Scholars Association and clearly defined the divergence within the Sunni political spectrum. Al-Jaafari's office praised Abdul-Hamid's Iraqi Islamic Party last week for condemning terrorism and political assassinations.

"At 4 a.m. today, American soldiers attacked my house from all directions," Abdul-Hamid said, looking tired after returning to his disheveled home. "They blew up doors and took me and my three sons. They blindfolded me and put me in a helicopter and took me someplace. They interrogated me all day. Then they let me go."

When asked if he was questioned about sectarian matters, Abdul-Hamid said no. He added that he believed his sons also had been released and were returning home. Eight guards were detained, including one who had a minor gunshot wound, according to Nazar Hamdan Tokan, a member of the Iraqi Islamic Party.

"This is a provocative and foolish act," said Iyad Samarrai, secretary-general of the party. "At a time when Americans say they are keen on real Sunni participation, they are now arresting the head of the only Sunni party that calls for a peaceful solution and has participated in the political process."

Some Sunnis said they believed Abdul-Hamid's arrest was an attempt by Shiites to keep Sunnis out of the government by disrupting new national elections scheduled for late this year.

"The goal of this incident is to delay the [December] elections and not to include the Sunnis," said Mohammed Hussein Ali, head of the Bakara tribe near Fallujah. "They want to push the country to sectarian war."

Message said to be

from insurgent leader

CAIRO, Egypt — Iraq's insurgent leader Abu Musab al-Zarqawi purportedly made an audio address to Osama bin Laden yesterday to assure the al-Qaida leader that he was in good health after being wounded in a fire fight with U.S. troops.

There was no way to confirm the voice was that of Jordanian-born terror leader al-Zarqawi. However, the recording was carried by a Web site frequently used by militant Islamic groups, and the voice sounded similar to that previously attributed to al-Zarqawi.

"I am sure you have heard through the media that I was wounded and treated in a Ramadi hospital. I would like to assure you and the Muslim nation that these were pure allegations. It was a light wound, thank God. We are back fighting them in the land of the two rivers."

The speaker addressed the message as "a letter from a soldier on the firing line to his commander."

The speaker purporting to be al-Zarqawi asked bin Laden for guidance on conducting the insurgency.