BAGHDAD — Suspected Sunni insurgents ambushed a minibus carrying Iraqi police recruits near the Syrian border Monday, killing all 11 passengers, Iraqi officials said — the first deadly attack since Iraqi forces launched a major sweep against al-Qaida fighters in the region.

The hail of gunfire came hours after Iraqi officials said they arrested a man suspected of being al-Qaida in Iraq's chief leader in the northern city of Mosul, the terror network's most prominent urban stronghold.

The attack, the bloodiest in months against police, left the minibus riddled with bullets in the desert west of Mosul, where the crackdown has been centered. Some al-Qaida fighters are believed to have fled the city toward neighboring Syria.

Police discovered the bodies of the police recruits and their minibus near Baaj, a remote town 20 miles from the Syrian border, according to a provincial official in Baaj and a Mosul police officer. The policemen, most from Baaj, were returning from their recruitment camp, they said.

It appeared a large group of insurgents had ambushed the minibus with a spray of gunfire. Nine bodies, including the police driver's, were found still in the vehicle and two on the ground outside, the two officials said. They spoke on condition of anonymity because they were not authorized to talk to the press.

The provincial official said the attack had the hallmarks of al-Qaida in Iraq and could have been in retaliation for the Mosul crackdown, launched over a week ago. The U.S. military said it was looking into reports of the attack.

Until now, the Mosul sweep had seen almost no violence, even as U.S.-backed Iraqi soldiers and police conducted arrest raids in the city — a sign that militants had fled or were lying low. On Monday, the Defense Ministry announced the first death in the crackdown, a militant killed in Mosul. In past years, police recruits were a frequent target of Sunni insurgents. But there has not been a comparable attack against recruits since November.

U.S. and Iraqi forces have also been carrying out sweeps in areas around Mosul — including the desert around Baaj — to intercept fleeing fighters.

It was not immediately clear if the slaying of the police officers was a sign of Sunni insurgents regrouping from the crackdown or a target of opportunity for fighters trying to avoid capture.

In either case, it was a dramatic assault on police forces, who have been less of a target in recent months for Sunni insurgents. This year, al-Qaida in Iraq has focused its attacks more on groups Sunni tribal fighters known as Awakening Councils, which have been fighting alongside the Americans against al-Qaida. Numerous suicide bombings and other attacks have killed dozens of Awakening Council members this year.

In past years, police recruits were a frequent target of Sunni insurgents. But there has not been a comparable attack against recruits since November, when a suicide bomber on a bicycle killed 27 in Baqouba, northeast of Baghdad.

This year to date, at least 699 Iraqi security forces and Awakening Council members have been reported killed and 924 wounded, according to an Associated Press count, including 76 killed so far during May. This total includes Iraqi military, police and police recruits, as well as Awakening members.

During the same time period, at least 3,331 civilians were killed in war-related violence and at least 4,180 wounded.

Prime Minister Nouri al-Maliki launched the crackdown in Mosul in a bid to break the hold of al-Qaida in Iraq and other insurgents in the city, 225 miles northwest of Baghdad.

The U.S. military has described Mosul as al-Qaida in Iraq's last urban stronghold after the group lost control of cities in the western province of Anbar over the past year. Al-Qaida militants and other Sunni Arab insurgents have used Mosul, a key transport hub with highways to Baghdad and Syria, for suicide bombings and other attacks in northern and central Iraq.

Hours earlier, Iraqi officials said they had arrested a man suspected of being al-Qaida in Iraq's chief leader in Mosul. The U.S. military said it was looking into the report. Reports of high-level al-Qaida in Iraq arrests in the past have sometimes proven inaccurate.

Maj. Gen. Ahmed Taha, of the Iraqi Interior Ministry, identified the detainee as the terror group's "wali" — or "governor" — in Mosul, a title which would make him its top figure in the city and the Ninevah province where it is located.

A security official involved in the detention said the suspect, Abdul-Khaliq al-Sabawi, admitted in questioning to being the Mosul wali.

Al-Sabawi, a former brigadier in Saddam Hussein's military, fled Mosul before the crackdown and took refuge in the Sunni Arab city of Tikrit in Salahuddin province, 120 miles to the south, the official said.

Confessions by other militants captured in Mosul during the sweep led security forces to his hiding place, and he was brought back to Mosul for interrogation, according to the official, who spoke on condition of anonymity because he was not authorized to discuss the arrest.

Taha said only that al-Sabawi was arrested in Salahuddin province, without specifying where.

More than 1,300 people have been arrested in and around Mosul during the current operation, though 240 were cleared of suspicion and released, said Maj. Gen. Hussein Ali Kamal, the deputy interior minister for intelligence and security affairs.

Al-Maliki ordered the Mosul sweep after similar crackdowns against Shiite militiamen in the southern city of Basra and Baghdad's Shiite stronghold of Sadr City.