BAGHDAD — Shiite militants and police enraged by deadly truck bombings went on a shooting rampage against Sunnis in a northwestern Iraqi city yesterday, killing as many as 70 men execution-style and prompting fears that sectarian violence was spreading outside the capital.

The killings occurred in the mixed Shiite-Sunni city Tal Afar, which had been an insurgent stronghold until an offensive by American and Iraqi troops in September 2005, when militants fled into the countryside without a fight. Last March, President Bush cited the operation as an example that gave him “confidence in our strategy.”

The gunmen roamed Sunni neighborhoods in Tal Afar through the night, shooting at residents and homes, according to police and a local Sunni politician. Witnesses said relatives of the Shiite victims in the truck bombings broke into Sunni homes and killed the men inside or dragged them out and shot them in the streets.

General Khourshid al-Douski, the Iraqi army commander in charge of the area, said 70 were shot in the back of the head and 40 people were kidnapped. A senior hospital official in Tal Afar, who spoke on condition of anonymity out of security concerns, said 45 men were killed.

Outraged Sunni groups blamed Shiite-led security forces for the killings. Prime Minister al-Maliki’s office ordered an investigation and the U.S.command offered to provide assistance.

Ali al-Talafari, a Sunni member of the local Turkomen Front Party, said the Iraqi army had arrested 18 policemen accused in the shooting rampage after they were identified by Sunni families. Shiite militiamen also took part, he said.

The revenge killings among Shiites in the religiously mixed city 260 miles northwest of Baghdad were triggered by truck bombings in Tal Afar on Tuesday that killed 80 people and wounded 185.

General Douski said one of the trucks exploded after the driver lured people in a predominantly Shiite neighborhood to the site by telling them he was distributing free flour from a humanitarian organization.

The bombing caused surrounding buildings to collapse, leaving huge piles of concrete and bricks dusted with white flour.

Videotaped footage from the scene was broadcast last night showing a man dead in the front seat of his car. Men and women carried the limp bodies of children powdered with flour. Others dug through the rubble with their bare hands in a search for survivors.

Meanwhile, President Bush and the Democratic-controlled Congress lurched toward a veto showdown over Iraq yesterday, the commander in chief demanding a replenishment of war funding with no strings and Rep. Nancy Pelosi counseling him, “Calm down with the threats.”

In related news, King Abdullah denounced the American military presence in Iraq yesterday as an “illegitimate foreign occupation” and called on the West to end its financial embargo against the Palestinian Arabs.

The Saudi monarch’s speech was a strongly worded lecture to Arab leaders that their divisions had helped fuel turmoil across the Middle East, and he urged them to show unity.