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Hadi Mizban, Associated Press
Baghdad municipality workers clean the site of a car bomb explosion in Baghdad’s Allawi neighborhood, Iraq, Monday, July 14, 2014. Parked car bombs killed civilians in commercial areas of Baghdad on Monday, as government forces and allied Sunni tribal fighters tried to dislodge militants from a small town north of the capital, officials said.

BAGHDAD — Government forces and allied Sunni tribal fighters battled to dislodge militants from a small town along the Tigris River on Monday, while authorities discovered 12 bloated bodies with gunshots to the head near another village north of the capital, officials said.

The clashes in Duluiyah are part of the Islamic State extremist group's larger offensive across Iraq as it tries to expand the territory under its control. The jihadis, along with other Sunni militants, have already seized control of much of northern and western Iraq, touching off the country's worst crisis since U.S. troops left in 2011.

Fighters from Islamic State group barreled into Duluiyah, some 80 kilometers (45 miles) north of Baghdad, on Sunday, and quickly seized the mayor's office, police station, local council and courthouse. They also blew up a bridge connecting the town with the nearby city of Balad.

The Iraqi military launched a counterattack, but the fighting bogged down and was still raging Monday, officials and a resident said.

Jassim Mohammed, who lives in Duluiyah, said dozens of militants in SUVs had pushed into the neighborhoods of Khazraj and Boujwar before facing stiff resistance from the Joubour tribe. The fighting Monday was with machine guns and rocket-propelled grenades, and there were casualties on both sides, Mohammed said.

He added that most of the tribesmen battling the militants are members of the local police force, which is largely composed of former soldiers from Saddam Hussein's army.

"They will not give up easily, the battles are fierce and ongoing," Mohammed said.

East of Duluiyah, authorities discovered the bodies of 12 men with bullet wounds to the head near the predominantly Sunni village of Nofal, police said. The bodies, which appeared to have been outside for a few days, were taken to the morgue in the nearby city of Muqdadiya.

It was not clear who the men were or why they were killed. But on Saturday there were heavy clashes between the army and Sunni militants who had seized at least partial control of a military base near Nofal. It is possible that the men could have been killed in a feud among Sunni militants.

But for many Iraqis, the discovery, just five days after 50 bodies were found in a field south of Baghdad, conjures up memories of the country's sectarian bloodletting of 2006 and 2007, deepening fears the nation could be heading down that path again.

Sunni-Shiite tensions have risen dramatically since the Sunni militant offensive began last month with the capture of the northern city of Mosul. The blitz has slowed since its initial burst, but the insurgents have vowed to push on to Baghdad.

The capital has seen several small scale bombings, but no major attacks, over the past month. The blitz has caused jitters in Baghdad, where Shiite militias have joined security forces in recent weeks to try to boost security in the city, although relatively minor attacks still happen almost daily.

On Monday, two car bombs exploded in commercial areas of Baghdad, killing at least seven people.

The deadliest attack took place in Baghdad's Allawi neighborhood, a predominantly Shiite district near the Green Zone that is home to many government offices and foreign embassies. A police official said four civilians were killed and 12 wounded in that blast.

He said the casualties could have been much worse, but the area was not crowded early Monday because of a state holiday to commemorate the 1958 Revolution that overthrew the monarchy.

A second vehicle packed with explosives blew up near a string of car dealerships in Baghdad's southeastern Bayaa area, killing at least three people and wounding eight, the official said. The explosion also damaged several cars.

All officials spoke on condition of anonymity because they were not authorized to brief the media.

Associated Press writers Bassem Mroue in Beirut, and Murtada Faraj in Baghdad contributed to this report.