Until Tuesday, the Education Ministry remained untouched by the car bombs that explode daily here. Insurgents had announced from mosque loudspeakers that the ministry was off-limits because of its benevolent mission, and they may also have been deterred by the buildings clustered around it: a high school, a primary school and a kindergarten.

So when a BMW sedan detonated outside the ministry building at 9:30 a.m., killing at least six people, those running fastest to the crater in the middle of the street were parents.

"I saw three cars were burning, and I saw all the glass of the windows was broken, and I saw the schoolmaster of the primary school telling the pupils to go home," said Mustafa Khateeb, 34, who was summoned from his university workplace by his sister, whose son was in the primary school.

"The children were crying and screaming," Khateeb said.

Meena Abdul Qader, 13, was in a classroom at the Hariri High School for Girls when the windows blew in and smoke filled the building.

"I saw five students in the classroom next door injured by the glass, but I don't know what happened to them because I ran away to my house," she said.

Twenty people were wounded in the attack, according to a spokesman for the Interior Ministry.

Two members of the Iraqi National Guard were killed in a separate car bombing in the northern city of Mosul. That attack, which targeted a military convoy carrying an Iraqi general, was carried out by an affiliate of al Qaeda in Iraq, the group led by Abu Musab Zarqawi, a Jordanian insurgent, according to a statement posted on a militant Islamic Web site.

A group of Iraqi militants holding aid worker Margaret Hassan threatened to turn her over to Zarqawi's group unless Britain withdrew troops from Iraq. The group was known as Monotheism and Jihad until Zarqawi pledged allegiance to Osama bin Laden last month.

The Arab satellite news channel al-Jazeera said the threat was contained in a new videotape, which the station declined to air because it was too distressing. The station did not elaborate, but Britain's Press Association news agency quoted Ireland's prime minister, Bertie Ahern, as saying it shows Hassan fainting while pleading for her life. Ahern, who had read a written summary of the video, said her abductors then throw water over her head and she is seen lying on the ground weeping.

Hassan, born in Ireland and married to an Iraqi, has lived in Baghdad for 30 years. She is the country director for CARE International.

"Margaret has no political associations," Ahern said in an appeal made with relatives of Hassan outside his Dublin headquarters. "She represents nobody but the vulnerable and the poor. Your quarrel is not with Margaret. Nor is it with the Irish people, who have been a firm friend of the Arab nations."

Zarqawi's group has cultivated a reputation for brutality. On Tuesday, the group posted video of the beheading of Shosei Koda, the Japanese backpacker whose body was recovered in a field last week wrapped in an American flag. Japan's government had rebuffed demands to withdraw the 550 troops it has in southern Iraq doing reconstruction work.

U.S. Embassy officials said they had no word on an American civilian kidnapped from a Baghdad house at dusk Monday. The unidentified man was abducted along with a Nepalese, a Filipino and three Iraqis by a gang of at least a dozen attackers. Two of the Iraqis, who had been working as guards, were found tied and blindfolded elsewhere in Baghdad on Tuesday, news services reported.

"No one's claimed responsibility or made any demands," an embassy spokesman said.

Meanwhile, saboteurs attacked two oil installations in the country's north. The damage will cut off exports from that part of the country for 10 days, news services quoted officials as saying.

One attack damaged a pipeline used for export. A second explosion targeted the Ghabaza oil field southwest of the city of Kirkuk.

Last week, insurgents in Fallujah had threatened to sabotage Iraq's oil infrastructure if their demands for cheap gasoline were not fulfilled. Dow Jones reported that Iraqi crude had fallen to less than half the storage capacity at Ceyhan, the Turkish port on the Mediterranean Sea where tankers are loaded.

Qader, the student, blamed the car bombing in Baghdad on "saboteurs who don't want Iraq to be developed. They don't want us to finish our schooling in peace."

Khateeb, who teaches dentistry at a Baghdad college, said the attack had been foreshadowed by warnings to the ministry's guards and leaflets warning residents. "I expected what happened today," he said. "I always warn my wife not to put the children near the windows."