Baghdad, Iraq ? Car bombs killed at least a dozen people in Baghdad and another major city Tuesday as pressure mounted on interim Prime Minister Ayad Allawi to avert a full-scale U.S. attack on the insurgent stronghold Fallujah.

There was no word on an American and two other foreigners abducted Monday in Baghdad, although the kidnappers freed two Iraqi guards also captured in the attack.

Kidnappers of aid worker Margaret Hassan threatened to turn her over to al-Qaida-linked militants notorious for beheading hostages unless Britain agreed within 48 hours to pull its troops from Iraq, Al-Jazeera television reported Tuesday.

Al-Jazeera broadcast a portion of a video showing a hooded gunman, and without sound. No group has claimed responsibility for Hassan’s kidnapping, and the broadcast showed no sign of any banner identifying who held her.

In London, Prime Minister Tony Blair’s office and the British Foreign Office both declined to comment on the reported demand. Britain has 8,500 troops in Iraq, the second-largest contingent after the United States.

In northern Iraq on Tuesday, saboteurs blew up an oil pipeline and attacked an oil well, violence that is expected to stop oil exports for the next 10 days, Iraqi oil officials said. Iraq’s oil industry, which provides desperately needed money for reconstruction efforts, has been the target of repeated attacks by insurgents.

At least eight people, including a woman, died early Tuesday when an explosives-laden car slammed into concrete blast walls and protective barriers surrounding the Education Ministry in Baghdad.

Ten others were injured, including a 2-year-old girl, according to Al-Numan Hospital. Officials at Baghdad Medical City Hospital reported two more deaths and 19 injured. Dr. Raed Mubarak said he was unsure whether some of the wounded were transferred from other hospitals.

In Mosul, 225 miles northwest of Baghdad, a car bomb exploded near a military convoy carrying an Iraqi general, killing four civilians and wounding at least seven soldiers.

A U.S. Army soldier guards the site of a car bomb explosion near an office of the Iraqi Ministry of Education in Baghdad, Iraq. The bomb was one of two Tuesday, the other wounding civilians and seven Iraqi soldiers in Mosul.

Iraqi police said the attack was an assassination attempt on Maj. Gen. Rashid Feleih, commander of a special task force, who was not injured. Feleih was apparently on his way to a news conference to talk about the role of the task force, according to police and media reports.

The violence came as American forces prepare for a major offensive against Fallujah and other Sunni militant strongholds north and west of Baghdad in hopes of curbing the insurgency so that national elections can be held in January.

U.S. forces have pounded insurgent positions around Fallujah almost daily, but American officials say the go-ahead for an all-out assault must come from Allawi, the interim prime minister.

However, new pressure mounted Tuesday on Allawi, a Shiite Muslim, to forego an assault and to continue negotiating with the hardline Sunni clerics who run the city, which has become a symbol of Iraqi resistance throughout the Arab world.

Mohammed Bashar al-Faidhi, spokesman of the Association of Muslim Scholars, said his clerical group would use “mosques, the media and professional associations” to proclaim a civil disobedience campaign and a boycott of the January elections.

“In the case of an incursion in Fallujah, there will be a call to boycott elections,” al-Faidhi said. “In case of an incursion, more deterrent steps will be taken.”

U.S. officials believe Fallujah is the stronghold of an al-Qaida faction led by Jordanian militant Abu Musab al-Zarqawi, whose followers are responsible for numerous car bombings and beheadings of foreign captives.