FALLUJA, Iraq, (Reuters) – Iraqi police placed the city of Falluja in a total lockdown on Wednesday, banning traffic and pedestrians as they hunted for what they said was a group of al Qaeda militants carrying out a bombing campaign.

Schools were closed, shops told to be shuttered and a curfew put in place from daybreak after explosions targeting police in the dusty city in the western desert province of Anbar, once the heartland of Sunni Islamist resistance to the U.S. invasion.

On Tuesday, a suicide bomber rammed his car into a police checkpoint, killing an officer and wounding nine other people at the south entrance to Falluja, 50 km (32 miles) west of Baghdad.

Two days before, two bombs which exploded in succession killed a police major and wounded another eight police officers in the centre of the city, shattering the city’s relative calm.

“We are investigating targets. We have information that they conducted a series of explosions,” police Colonel Mahmoud al-Issawi told Reuters.

“We want to root out those elements to avoid future explosions and to ensure security and stability in the city.”

The recent violence in Falluja pales when compared to the average 10 bombs a day that still explode in Baghdad and the near daily shootings and bombings by a still active Sunni Arab insurgency in the provinces of Diyala and Nineveh.

But Anbar was once in the grip of al Qaeda and other insurgents, who battled U.S. forces in some of the bloodiest fighting after the 2003 invasion to topple Saddam Hussein, and authorities are loath to let them back in again.

Anbar’s tribes eventually grew fed up with al Qaeda’s brutal version of Islamic law and turned on it in 2006, forming the now U.S.-sponsored Awakening Councils, which helped drive the insurgency to ground and led to a steep drop in violence. But police said they had intelligence suggesting the attackers planned an escalation.

“Outsiders who belong to al Qaeda have infiltrated from Diyala province and Mosul. Their aim is to conduct terrorist acts inside the city,” said police Lieutenant-Colonel Abdul-Aziz Saif.

Saif said a special police force from Ramadi, Anbar’s other large city, had come to Falluja to reinforce its police.

The curfew imposed on the city while police conducted raids turned Falluja into a ghost town.

A few shops were open. Pedestrians caught out in the open were told by police to go home. They fired shots into the air to clear those who resisted, witnesses said.

A roadside bomb in northwest Baghdad’s Shi’ite Kadhimiya district killed seven people and wounded 23 others on Wednesday.

Kadhimiya is home to one of Shi’ite Islam’s holiest shrines, and the blast bears the hallmarks of Sunni Islamist al Qaeda, which considers Iraq’s majority Shi’ites heretics and frequently targets the sect’s mosques and religious festivals.

Violence has dropped sharply in Iraq over the past year, and U.S. President Barack Obama lauded the increased security during a visit to Baghdad on Tuesday. Yet al Qaeda and other insurgents are still capable of launching frequent large-scale attacks.

An apparently coordinated series of seven car bombs ripped through Baghdad killing 37 people on Monday.