U.S. soldiers arrested five Iraqis on Friday after a roadside bomb struck a U.S. convoy north of the capital. A series of nighttime explosions shook the volatile area of Fallujah, but the U.S. military said they caused no casualties.

American troops sealed off the area and arrested the Iraqis after the roadside bomb went off Friday morning in Khalis (search), 50 miles north of Baghdad. A civilian SUV was damaged and three passengers may have been injured, witnesses said.

A U.S. Army spokesman also said a mortar was fired Thursday night at the Forward Operating Base St. Mare in Fallujah, but it caused no casualties or damage to the post. Witnesses, however, said they heard multiple explosions.

In nearby Ramadi (search), witnesses said a pair of Army Humvees were attacked with RPGs as they tried to visit a police station. Hatif Mahmoud, who saw the attack, said there didn't appear to be any casualties, but a window on one of the Humvees was broken.

The violence came a day before the deadline for members of the Iraqi Governing Council (search) to approve an interim constitution, a key step in U.S. plans for transferring power to an Iraqi government on June 30.

Mahmoud Othman (search), a Sunni Kurd member of the Governing Council, said, however, that it was unlikely the draft will be finished by Saturday. He said major differences remain among the drafting committee members, including the role of Islam, Kurdish autonomy and how to constitute a new administrative body to take power June 30.

On Thursday, Iraq's most prominent Shiite cleric, Grand Ayatollah Ali al-Husseini al-Sistani (search), said he would accept a weak, unelected government to rule after the June 30 deadline if elections are scheduled as soon as possible thereafter and the United Nations guarantees no more postponements.

It is now up to the United Nations, the U.S.-run occupation authority and the Iraqi leadership to decide how to constitute such a government, not only acceptable to the country's majority Shiites but to the Sunni Arabs, Kurds, Turkomen and Christians as well.

The United States would prefer expanding the 25-member Iraqi Governing Council to include more Sunnis and other groups to enhance the body's legitimacy among Iraq's 25 million people.

Al-Sistani had initially demanded elections to choose a transitional legislature, which in turn would appoint a government. The elderly, Iranian-born cleric rejected that blueprint because the lawmakers would be selected in regional caucuses rather than by the voters.

In the Shiite holy cities of Najaf and Karbala, meanwhile, tens of thousands of Shiite men, including many Iranian pilgrims, performed traditional self-flagellation rituals Friday as part of the feast of Ashoura (search), which marks the killing of the Shiite saint, Imam Hussein.

This year's feast, which continues into next week, is the first Ashoura commemoration since the fall of Saddam Hussein's regime. Security is tight in the holy cities to prevent sectarian attacks.

"It is expected that terrorist groups will make attacks in order to show that the situation, not only in this city, but in all Iraq, is not stable," Abed Mehdi al-Salami said in Karbala. "They are doing this for the sake of their own political ends."

In Fallujah, hundreds of residents said they would march Friday to protest what they said were attempts by the U.S. army to detain a local imam.

In a call to attendees at the Saad Bin Abi Waggas mosque, attendees were urged through loudspeakers to march in a show of support and solidarity for Imam Abdullah al-Janabi.

A call by the Associated Press to the 82nd Airborne, which oversees the area, rang unanswered.

In other developments:

— Three rocket-propelled grenades were fired Thursday night at an office of the Patriotic Union of Kurdistan, a leading Kurdish party, in the northern city of Kirkuk, killing one person, security chief Gen. Sherko Shaker said.

— Security forces caught a non-Iraqi wearing an explosive suicide vest in a Kirkuk market on Thursday, apparently planning to carrying out a bombing, a security official said.

— In Irbil, the joint security committee of Iraq's two main Kurdish parties — the Kurdish Democratic Party and Patriotic Union of Kurdistan — said Friday they will start banning cars without license plates, or documents proving they were imported in the country before April 2003, in Kurdish-controlled areas in a bid to stem possible suicide attacks.

— Some 130 Japanese soldiers left Kuwait for Iraq early Friday, on their way to a mission which will eventually involve up to 1,000 ground, air and naval forces. They will join a unit of 100 Japanese soldiers in Samawah, about 230 miles southeast of Baghdad, where they are working to supply Iraqis with clean water, rebuild schools and bolster local hospitals.