The U.S. Embassy and two consulates in Pakistan reopened Monday but it was not clear when business would resume at the consulate office in Karachi, where a deadly car bomb killed 12 people and injured 44 last week.

More than two dozen FBI agents joined Pakistani investigators over the weekend in videotaping and photographing the area to reconstruct Friday's massive blast, which killed 11 people instantly. A police constable injured in the blast died Sunday.

No Americans were killed in the attack but a U.S. Marine guard and five Pakistani consulate employees were injured. All were expected to survive

The U.S. Embassy in Islamabad and consulates in Lahore and Peshawar, shut down after the attack Friday, reopened for business Monday.

"With the exception of the Consulate General in Karachi, all U.S. Mission facilities in Pakistan, including the embassy's consular section are operating normally today," an embassy spokeswoman said Monday.

She said a decision on reopening the Karachi consulate was expected, perhaps as early as Monday, following an assessment of the compound's structural integrity.

A previously unknown group called "al-Qanoon," or "The Law," claimed responsibility for the attack. The group faxed a message Sunday to the Pakistani newspaper Ummat calling on President Pervez Musharraf to resign. The group also threatened more attacks.

Police said they are taking al-Qanoon seriously. U.S. officials in Washington say they suspect Al Qaida or Islamic extremist groups affiliated with it, but have no direct evidence. Several Pakistani groups in Karachi have ties to Usama bin Laden's terror network and are angry that Musharraf sided with the United States in the war against terror.

Police have questioned three people so far, though no one has been taken into custody, said investigator Manzoor Mughal. The witnesses include a religious school student, a security guard and an auto mechanic, he said.

The student, identified as Riaz Uddin, was walking near the area when he was injured in the blast. Interviewed in the hospital, he told police he was a student at the Jamia Faruqia madrassa, an Islamic school.

Private security guard Sharif Ajnabi was in the park across the street from the consulate when the bomb went off.

The mechanic, who was not identified, works at a car shop owned by one of the victims of the blast, Syed Shafat Husain. Husain and his niece, Aliyah Warsi, a physician from Kenya, were killed as they left a hotel nearby, where they had booked a hall for her marriage to a Pakistani man.

The explosion blew a gaping hole in the wall surrounding the heavily guarded consulate, damaged or destroyed 18 cars, shattered windows a block away and sent debris flying half a mile. The devastation made it difficult to piece together events leading up to the bombing.

Officials first said they thought a suicide bomber was responsible. But attention has shifted to a driver's training school car that was carrying an instructor and three female students. Police said the bomb may have been stashed in the vehicle by someone who knew it would pass by the consulate and who detonated the explosives by radio from nearby.

The attack — the fourth against foreigners in Pakistan since January — also prompted the U.S. government to consider scaling back diplomatic staff in a country on the front line of the war against Al Qaida.