TAL AFAR, Iraq – Insurgents staged a classic guerrilla retreat from Tal Afar yesterday, melting into the countryside through a network of tunnels to escape an Iraqi-American force that reported killing about 150 rebels while storming the militant bastion.

With the city swept clear of extremists for the second time in a year, Iraqi and American military leaders vowed to redouble efforts to crush insurgents operating all along the Syrian frontier and in the Euphrates River valley.

“Tal Afar is just one piece of an overarching operation. We are not going to tolerate a safe haven anywhere in Iraq,” the deputy chief of staff for coalition forces in Iraq, Army Major General Rick Lynch, said.

As Baghdad kept a border crossing into Syria closed about 60 miles west of Tal Afar, Defense Minister Sadoun al-Dulaimi issued a warning: “The Syrians have to stop sending destruction to Iraq. We know the terrorists have no other gateway into Iraq but Syria.”

America and Iraq routinely charge that Syria’s government does little to stop the flow of Arab fighters across the border. Syrian leaders contend they are doing all they can.

While insurgents were retreating from Tal Afar, militants elsewhere killed one American soldier and a British soldier in separate roadside bombings yesterday and assassinated an official in Iraq’s Interior Ministry.

A Task Force Liberty soldier was killed and two were wounded during a pre-dawn patrol near Samarra, 60 miles north of the capital. At least 1,897 American personnel have died since the Iraq war started in March 2003, according to an Associated Press count.

In the southern city of Basra, a British soldier was killed and three were wounded in an attack on their convoy, the British Ministry of Defense said in London. Britain has reported at least 96 deaths since the war began.

Police said Major General Adnan Abdul Rihman, the Interior Ministry’s director of police training, was fatally shot in front of his west Baghdad home as he waited for a ride to work.

Tal Afar had been cleared of militants a year ago, but insurgents moved back after American troop numbers in the area were reduced.

American warplanes bombed several suspected militant targets in the city last week, and the long-expected assault to again take Tal Afar was launched early Saturday by 5,000 Iraqi soldiers backed by a 3,500-strong American armored force.

By last night, the joint force reported 156 insurgents killed and 246 captured. It said troops found a big bomb factory, 18 weapons caches, and the network of escape tunnels beneath Tal Afar’s ancient Sarai neighborhood.

After stiff initial resistance Saturday, insurgents fell back and their stronghold was nearly deserted when the joint force moved in.

“The terrorists had seen it coming [and prepare] tunnel complexes to be used as escape routes,” General Lynch said.

As troops continued house-to-house searches in Tal Afar, a group claiming to be an offshoot of Al Qaeda in Iraq said it would strike American positions and the Iraqi government in Baghdad with “chemical and unconventional weapons … unless the military operations in Tal Afar stop within 24 hours.”

The Mujahedeen of the Victorious Sect posted the threat on an Islamic Web site known as a clearinghouse for terrorist messages. The claim could not be authenticated, but it was the second such threat since Friday, when Al Qaeda in Iraq said it would use chemical weapons against Baghdad’s Green Zone, which houses the Iraqi government, parliament, and the American Embassy.

The American military, meanwhile, said it killed a key Al Qaeda leader, identified only as Abu Zayd, during a raid on a safe house in Mosul, 45 miles east of Tal Afar. Four other Al Qaeda militants were captured.

Mr. al-Dulaimi said the offensive in Tal Afar would be a model as his forces soon thrust farther west toward the Syrian border and south into the Euphrates valley. “After the Tal Afar operation ends, we will move on Rabiyah [on the Syrian border] and Sinjar [a region north of nearby Mosul] and then go down to the Euphrates valley,” he said.

“We are warning those who have given shelter to terrorists that they must stop, kick them out or else we will cut off their hands, heads, and tongues as we did in Tal Afar,” Mr. al-Dulaimi added, apparently using figurative language.

He said only five government soldiers were killed and three wounded in the Tal Afar fighting, the biggest military operation in Iraq for months.

Most of Tal Afar’s residents fled before the fighting, and tens of thousands are living in tent cities to the north and east. Food, water, and medical supplies are scarce.

“This camp is suffering from the lack of medicine. I need an ambulance to evacuate the critical cases,” the only physician at a camp near the village of al-Alouliyah, Dr. Abdullah Jassem, said.

Women and children lined up with bowls waiting for small rations of rice, chicken, and tomato gravy.