Suspected Sunni militants struck in and around Baghdad on Wednesday, killing 17 people including 11 soldiers and policemen, and injuring about 40 in three separate attacks, including two suicide bombings, according to police and hospital officials.

The largest of Wednesday's attacks was in the turbulent Youssifiyah district south of Baghdad where a suicide car bomber hit an army checkpoint, killing six soldiers and injuring 16, including 10 civilians and six soldiers.

Earlier in Baghdad's upscale Mansour district, a car bomb near a cluster of shops killed six civilians and wounded 13. Minutes later, a suicide bomber blew himself up at the entrance of a nearby police station as officers were rushing out to the site of the first attack, killing five and injuring 10, all policemen.

The officials spoke on condition of anonymity because they were not authorized to speak to the media.

There was no immediate claim of responsibility for the attacks, but they all bore the hallmarks of the Islamic State group, whose fighters control about a third of the country after they blitzed across much of the north and west of Iraq this year.

Elsewhere in Iraq, government forces backed with Shiite militiamen are continuing to meet tough resistance from Islamic State fighters in the refinery town of Beiji, a day after they pushed militants out of the town center, a senior military official reached there by telephone said Wednesday.

The official said reinforcements have reached Beiji, 250 kilometers (155 miles) north of Baghdad, to protect areas of the town now under government control. Booby-trapped houses and roadside bombs however were hindering their advance toward the northern and northwestern parts of the town, where Iraq's largest refinery is located.

The official spoke on condition of anonymity because he was not authorized to brief reporters.

Lifting the siege of the refinery, which sits inside a sprawling complex whose capacity of some 320,000 barrels a day accounts for a quarter of Iraq's refining capacity, was likely the next objective in the campaign to rid Beiji of the militants.

When fully retaken, the strategic town will likely be a base for a future push to take back Saddam Hussein's hometown of Tikrit just to the south, one of the main prizes overrun by the extremists last summer.