BAGHDAD — A member of an extremist cell believed to be behind a suicide attack that killed more than 20 people including three U.S. Marines has been arrested, the U.S. military said today.

U.S. spokesmen said it was unclear if the suspect, who was not identified, was directly involved in planning the attack that happened yesterday in the town of Karmah in Anbar province about 30 miles west of Baghdad.

A suicide bomber reportedly dressed in a police uniform detonated an explosive belt during a meeting of tribal sheiks opposed to al-Qaida in Iraq. In addition to the Marines, two Iraqi interpreters, the local mayor and several key tribal figures were killed.

The attack occurred two days before U.S. officials planned to formally hand over security responsibility for Anbar to the Iraqis, marking a major milestone in the transformation of a province that had been the most violent in Iraq.

U.S. authorities announced today they were postponing the handover ceremony because of weather forecasts calling for high winds and sandstorms, which would ground aircraft and make it impossible for dignitaries to attend.

Lt. Col. Chris Hughes, spokesman for U.S. forces in Anbar, said the U.S. had been planning to delay the ceremony based on weather forecasts before yesterday's attack.

Anbar, which extends from the western outskirts of Baghdad to the borders of Jordan, Syria and Saudi Arabia, will be the 10th of Iraq's 18 provinces to return to Iraqi security control. The other nine provinces are dominated by Shiites or Kurds.

Although Anbar is far quieter than in previous years, the Karmah attack shows that extremists, including al-Qaida in Iraq, remain a threat, albeit at a diminished level.

Also today, Iraq's Higher Judicial Council announced that a senior judge was assassinated by drive-by shooters while traveling in eastern Baghdad.

Judge Kamil al-Showaili was driving home yesterday when the attack occurred, the council said. He was the head of one of Baghdad's two appeals courts.

To the south, Iraqi security forces said they arrested two municipal officials in Maysan province for allegedly "violating the law."

Iraqi forces have launched a crackdown in the province and its capital city of Amarah to rid the area of Shiite militias. Followers of anti-American cleric Muqtada al-Sadr claim the operation is aimed at weakening their movement before provincial elections expected this fall.

In Baghdad, Iraqi authorities also announced they have restored the bust of Abu Jaafar Al-Mansour, the 8th-century founder of city. Saddam Hussein had often compared himself to al-Mansour.

A blast damaged the monument in Baghdad's Mansour district in October 2005, a day before Saddam went on trial for killing Shiite Muslims in Dujail — a charge for which he was later hanged.

Many Sunnis believed Shiite extremists were responsible for damaging the monument.