BAGHDAD, Iraq - A pair of car bombs exploded near government offices in the Iraqi capital today, killing 18 people and wounding three dozen others, while insurgent attacks against the nation's nascent security forces left at least eight others dead, officials said.

The near-simultaneous explosions outside an Interior Ministry office in a southeastern Baghdad neighborhood sent large plumes of smoke rising over the city and threw passers-by to the ground, witnesses said. U.S. military helicopters swooped overhead.

After clearing the area, U.S. forces detonated a third car that apparently failed to explode earlier, police said.

Ali Ahmed, 28, said he was selling ice cream from his stall when he heard an explosion, followed by gunfire and another explosion.

"My stall was partially destroyed because of this terrorist act," he said. "Some people have lost their lives. As for me, I have now lost my source of income."

The explosions blew out the windows of nearby restaurants in an upscale neighborhood of Baghdad, near the heavily fortified Green Zone. Panicked students from a nearby secondary school wept and shouted that they weren't going to attend classes anymore, waiting in the street for school buses or relatives to pick them up.

Interior Ministry official, Capt. Ahmed Ismael, said the first two blasts killed 18 and wounded 36. One government worker said five garbage collectors he was supervising were killed.

Insurgents kept up attacks today against Iraq's security forces, which the U.S. military says must be able to impose a level of calm in the country before American troops can depart.

Gunmen hit police patrolling near the central Iraq city of Baqouba, killing one officer and wounding three others, Lt. Col. Muthafar al-Jubori said.

In the capital, attackers shot and killed 1st Lt. Firas Hussein in the head and torso as he made his way to work at Iraq's intelligence service, police Maj. Mousa Abdul Karim said.

In Kirkuk, seven gunmen riding in two vehicles fired on the police station just south of Kirkuk shortly after dawn, killing five police officers and one civilian, police Brig. Sarhat Qadir said.

On Wednesday, an American was shown at gunpoint on a videotape aired by Al-Jazeera television, two days after he was kidnapped from a water treatment plant near Baghdad. The station said he pleaded for his life and urged U.S. troops to withdraw from Iraq.

The U.S. Embassy said the man on the video appeared to be Jeffrey Ake, a contract worker who was kidnapped around noon Monday. Ake - the 47-year-old president and CEO of Equipment Express, a company that manufacturers bottled water equipment - is the latest of more than 200 foreigners seized in Iraq in the past year.

President Bush's press secretary, Scott McClellan, said there would be no negotiating with the kidnappers.