BAGHDAD (AP) – A spree of revenge killings Wednesday after bombings in a mixed Shiite-Sunni city was the latest – and most ominous – sign that sectarian and tribal warfare is spreading across Iraq, opening new fronts for U.S. and Iraqi forces already stretched thin by efforts to calm Baghdad.

The carnage in Tal Afar, about 260 miles northwest of Baghdad, was a piece in an alarming and increasingly complex bloodletting nationwide: Sunnis fighting Sunnis west of Baghdad, Shiites battling Shiites in the deep south and Shiites against Sunnis in three towns on the southern fringes of the capital.

Tal Afar, in Iraq’s northwestern wheat belt, and the three towns in the fertile band of land between the Tigris and Euphrates rivers south of Baghdad had no history of major Sunni-Shiite strife until the U.S.-Iraqi security crackdown in the capital began six weeks ago.

The recent outbreaks of sectarian bloodshed marked what could be a significant acceleration toward a full-fledged internal war among Sunni and Shiite extremists.

“Security, as you can see, is still deteriorating in the country and sectarianism is unfortunately prevailing,” former Prime Minister Ayad Allawi, a Shiite, told The Associated Press on Wednesday.

U.S. and Iraqi officials have said that ridding Baghdad of its relentless sectarian violence would have a calming effect on the rest of the country, giving Prime Minister Nouri al-Maliki breathing room to impose government authority in hot spots outside the capital.

But the U.S.-Iraqi security sweep through Baghdad, which has had modest success since its launch Feb. 14, appears to have forced Sunni insurgents, al-Qaida in Iraq fighters and Shiite militiamen to take their fight to regions where there are fewer U.S. and Iraqi troops.

“The security plan in Baghdad has fragmented the terrorist network,” said Reda Jawad Taqi, a lawmaker and a senior leader of the Supreme Council for the Islamic Revolution in Iraq, the country’s largest Shiite political party. “It’s like a beehive: When disturbed, the bees fly everywhere.”

The violence in Tal Afar was the most ominous sign that sectarian violence may be taking root outside Baghdad, where it had been largely contained.

Tal Afar was a stronghold for insurgents until a U.S.-Iraqi offensive drove them off without a fight in September 2005, leading President Bush last March to cite the operation as an example that gave him “confidence in our strategy.”

But attacks inside the city have continued.

Enraged by truck bombings that killed at least 80 people and wounded 185 Tuesday, Shiite militants and off-duty policemen went on a killing spree that lasted into Wednesday and left as many as 70 Sunnis dead in the streets, many executed with a gunshot to the back of the head.

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

Outraged Sunni groups blamed Shiite-led security forces for the killings. 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.

Tal Afar isn’t alone.

Over the past week, supporters of a Shiite militia, the Mahdi Army, clashed with gunmen from Fadhila, a Shiite party, in the southern city of Basra, raising the prospect of a wider Shiite-on-Shiite conflict in a region of Iraq that had been relatively quiet under British control.

In the three mixed towns south of Baghdad – Iskandriyah, Haswa and Mahaweel – Shiite and Sunni mosques have been hit in tit-for-tat attacks. At least 13 people were killed, including 11 who perished in a suicide truck bombing at a Shiite mosque Saturday.

Quiet has returned to the towns, but flyers plastered to Sunni front doors, warning them to leave Iskandriyah or be killed, portend more violence.

Security in the three towns, near to one another and about 30 miles south of Baghdad, is extremely important. They sit at the gateway to the Shiite south, astride roads used by millions of pilgrims headed to the holy cities of Karbala and Najaf.

“All the requirements of a civil war are in place,” Mustafa al-Ani, a Dubai-based expert on Iraq, said in a telephone interview. “Civil war practices already are taking place, but the war will formally start when the Americans fail in Baghdad and begin to disengage.”

The Pentagon said in a report this month some of Iraq’s violence constituted civil war, but that the term did not fully describe the country’s complex situation.

Iraqi officials routinely dismiss such assessments and try to explain away the savagery gripping parts of the country as the work of al-Qaida in Iraq.

Whatever name is given to the violence, it is likely going to get worse with an escalating conflict among Sunnis in areas west and north of Baghdad. The government had hoped Sunni tribal militias it now backs would triumph over al-Qaida and its network of local Sunni supporters in the vast area.

But the government’s divide-and-rule strategy there has been weakened by a series of al-Qaida suicide bombings in recent weeks and the assassination of senior tribal figures who were believed at odds with the terror group or ready to enter talks with the U.S. about joining the political process.

In the latest such reprisal, a military leader from the 1920 Revolution Brigades, a major Sunni insurgent group thought to have held secret talks with the Americans, was killed Tuesday in an area west of Baghdad. Al-Qaida was blamed for the killing.

Harith Dhaher al-Dhari also was the son of a key tribal chief whose followers are thought to be divided between backing al-Qaida and the tribal militias fighting the terror group.

AP-ES-03-28-07 1756EDT