BAGHDAD, Iraq – A car bomb exploded in a jammed commercial district yesterday, turning the sky gray as shops and restaurants caught fire in the most deadly of a string of attacks that killed 21, including a general and colonel who were assassinated.

Iraqis expressed growing fury at the relentless bloodshed, throwing stones at police and American forces who came to the scene of the bombing. More than 90 were also wounded in yesterday’s violence.

The attacks came as American troops were in the midst of a major offensive near the Syrian border, 200 miles northwest of Baghdad. Fierce clashes were reported with insurgents on the outskirts of the town of Qaim, where angry residents lashed out at American forces.

“They destroyed our city, killed our children, destroyed our houses. We have nothing left,” one man in Qaim told Associated Press Television News. He did not give his name and hid his face with a scarf to address the camera.

Families were fleeing in trucks packed with luggage, and APTN footage showed plumes of smoke rising from the town. America has pounded the area with air strikes, artillery barrages, and gunfire in the first days of the offensive aimed at rooting out followers of Iraq’s most wanted militant leader, Abu Musab al-Zarqawi.

Five more American troops died in Iraq, two during the offensive Wednesday and three others when their convoys hit roadside bombs yesterday in Baghdad and surrounding areas, the American military announced. At least 1,611 members of the American military have died since the beginning of the Iraq war in March 2003, according to an Associated Press count.

More than 420 people have died in the two weeks since Iraq’s first democratically elected government was announced. At the Pentagon, the chairman of the Joint Chiefs of Staff, General Richard Myers, indicated yesterday that the insurgency could last for many more years.

“This requires patience,” he said at a news conference. “This is a thinking and adapting adversary … I wouldn’t look for results tomorrow. One thing we know about insurgencies, that they last from three, four years to nine years.

“What we’re seeing is really an attempt to discredit this new Cabinet and new government,” General Myers said. “This is, the most cases, Iraqis blowing up other Iraqis. And I don’t [know] how they expect to curry favor with the Iraq population when we have Iraqi-on-Iraqi violence.”

Scores of Iraqis in Baghdad vented their frustration at the nonstop violence, beating two Iraqi photographers and throwing rocks at Iraqi police and American forces at the site of the bloody car bombing near a market, cinema, and mosque.

The American and Iraqi troops fired in the air to disperse the crowd, according to an Associated Press photographer at the scene.

The blast, which set fire to shops, restaurants, and cars, killed 17 Iraqis and injured 81, including women and children, police said. About 15 minutes later, the fuel tank of a burning car also exploded, wounding three more people, police said.

In all, four car bombs hit Baghdad yesterday, two of them suicide attacks, an American military spokesman, Master Sergeant Greg Kaufman, said. At least two of the attacks targeted American patrols, he said, but he had no immediate word on casualties. Police said a suicide car bomber targeting an American convoy on a highway injured two civilian bystanders. Another car bomb in eastern Baghdad wounded three civilians, the American military said.

Elsewhere in the capital, insurgents assassinated Colonel Fadhil Mohammed Mobarak on his way to work at the Interior Ministry, and Brigadier General Iyad Imad Mahdi, who worked at the Defense Ministry, police said. Mr. al-Zarqawi’s Al Qaeda group in Iraq claimed responsibility for Mobarak’s death in an Internet posting. The claim could not be verified.

Two more car bombs exploded in Kirkuk, about 180 miles north of Baghdad, police said. One blast occurred near a police station, killing two people and wounding two, authorities said. The other occurred at a site where explosives experts were dismantling a homemade bomb and two explosive experts were wounded, police said.

The Sunni militant Ansar al-Sunnah Army claimed responsibility for both Kirkuk attacks on its Web site, claims that also could not be verified.

Near the Syrian border, hundreds of American troops searched sparsely populated desert outposts house by house for insurgents as Operation Matador entered its fifth day.

Residents reached by telephone in the villages of Karabilah and Saadah reported hearing heavy bombardments in the morning.

On the outskirts of Qaim, a group of masked gunmen armed with machine guns were defiant.

“We will fight whoever comes, whether they are American or Arab,” one of them told APTN.

The offensive was launched after American intelligence showed large numbers of insurgents had moved into the northern Jazirah Desert following losses in Fallujah and Ramadi, further east. The area is believed to be a staging ground for foreign fighters crossing into Iraq from Syria along ancient smuggling routes.

The American military has confirmed five Marine deaths so far and says about 100 insurgents have been killed in the operation – one of the largest American offensives since Fallujah was reclaimed from militants.