BAGHDAD (AP) – Shiite militants and police enraged by massive truck bombings in the northwestern town of Tal Afar went on a revenge spree against Sunni residents there Wednesday, killing as many as 60 people, officials said.

The gunmen began roaming Sunni neighborhoods in the city, shooting at residents and homes, according to police and a local Sunni politician.

Ali al-Talafari, a Sunni member of the local Turkomen Front Party, said the Iraqi army had arrested 18 policemen accused of being involved after they were identified by the Sunni families targeted. But he said the attackers included Shiite militiamen.

He said more than 60 Sunnis had been killed, but a senior hospital official in Tal Afar put the death toll at 45, with four wounded.

The hospital official, who spoke on condition of anonymity due to security concerns, said the victims were men between the ages of 15 and 60, and they were killed with a shot to the back of the head.

Police said earlier dozens of Sunnis were killed or wounded, but they had no precise figures, and communications problems made it difficult to reach them for an update. The shooting continued for more than two hours, the officials said.

Army troops later moved into the Sunni areas to stop the violence and a curfew was slapped on the entire town, according to Wathiq al-Hamdani, the provincial police chief and his head of operations, Brig. Abdul-Karim al-Jibouri.

“The situation is under control now,” said Mr. al-Hamdani. “The local Tal Afar police have been confined to their bases and policemen from Mosul are moving there to replace them.”

Tal Afar, located 260 miles northwest of Baghdad, is in the province of Ninevah, of which Mosul is the capital. It is a mainly Turkomen city with some 60 percent of its residents adhering to Shiite Islam and the rest mostly Sunnis.

The violence came a day after two truck bombs shattered markets in the city, killing at least 63 people and wounding dozens in the second assault in four days. After Tuesday’s bombings, suspected Sunni insurgents tried to ambush ambulances carrying the injured out of the northwestern city but were driven off by police gunfire, Iraqi authorities said.

The carnage was the worst bloodshed in a surge of violence across Iraq as militants on both sides of the sectarian divide apparently have fled to other parts of the country to avoid a U.S.-Iraqi security crackdown, raising tensions outside the capital.

The city was an insurgent stronghold until an offensive by American and Iraqi troops in September 2005, when rebel fighters fled into the countryside without a battle. Last March, President Bush cited the operation as an example that gave him “confidence in our strategy.”

But even though American and Iraqi forces put up sand barriers around Tal Afar to limit access, the city has suffered frequent insurgent attacks.

Meanwhile, hundreds of Iraqis detained in the American-led security crackdown in Baghdad are being held in two detention centers designed to hold at most a few dozen people, The New York Times reported Wednesday, citing an Iraqi monitoring group.

The report said 705 people were packed into an area built for 75 at one of the detention centers, in the town of Mahmudiya, south of Baghdad. The other center, on Muthana Air Base, held 272 people, including two women and four boys, in a space designed to hold about 50.

Officials from the monitoring group said they did not know the sectarian composition of the detainee populations.

Also Wednesday, explosions struck the government center in Fallujah, west of Baghdad, but there was no immediate word on casualties, officials said. Major Jeff Pool, a Marine spokesman in the area, said initial reports indicated that two suicide car bombers had attacked the building but detonated their explosives at the gates.