Baqouba, Iraq ? Until dawn broke, officials did not think of Muqdadiyah as an especially vulnerable place. Police occasionally raided nearby villages, as they did last weekend, hauling rebel suspects to cells in a courthouse compound in the city center.

At 5:45 a.m. Tuesday, masked men came to break them out. Descending from a dozen cars and pickup trucks laden with mortars and grenades, they surrounded the compound and blasted away, killing at least 17 police officers and guards and freeing 33 prisoners in one of Iraq’s boldest insurgent raids in months.

The highly coordinated frontal attack, which featured car bombs to repel reinforcements, was a potent reminder of the Sunni-led insurgency’s capacity to strike at Iraqi government and U.S. targets, despite almost constant sweeps against their forces and President Bush’s frequent assertions of progress in combating the insurgency.

In 90 minutes of fighting, the rebels destroyed 12 police cars and set fire to the courthouse and adjacent police station, holding off outnumbered U.S. and Iraqi forces. Reinforcements, delayed by insurgent booby traps, eventually chased down some of the insurgents, capturing eight as they fled in two vehicles.

Six of the attackers were killed, the U.S. military said, and 18 policemen and two U.S. soldiers were wounded.

The raid came as U.S. and Iraqi forces had concentrated in recent days on guarding against sectarian attacks against the 2 million Shiite pilgrims who gathered in the southern holy city of Karbala this week to mark the 40th and final day of the annual mourning period for Imam Hussein, grandson of the Prophet Mohammed.

Iraqi policemen look at their damaged vehicle at a police station in Muqdadiyah, Iraq, 60 miles north of Baghdad. Insurgents stormed a jail at dawn Tuesday in the Sunni Muslim heartland north of Baghdad, killing at least 15 police officers and a courthouse guard.

Instead, the insurgents aimed their deadliest strike about 60 miles north of Baghdad, in Muqdadiyah, an ethnically mixed city of 200,000 with a Sunni majority. Rebel forces also killed a policeman in Baqouba with a bomb, and fatally shot an American soldier on patrol in western Baghdad.

In an Internet posting, the military wing of the Mujaheddin Shura Council, a Sunni insurgent group, claimed responsibility for the attack in Muqdadiyah.