Iraqi federal policemen stand guard at a checkpoint in Basra, Iraq’s second-largest city, 340 miles (550 kilometers) southeast of Baghdad, Iraq, Thursday, Jan. 2, 2014. The Iraqi government has tightened its security measures after security forces have arrested, Wathiq al-Batat, a controversial Shiite cleric who leads an Iranian-backed militia called Mukhtar Army. (Nabil al-Jurani/Associated Press)

Security forces and allied tribesmen on Thursday battled to put down al-Qaeda-linked gunmen who, in a coordinated surge, ran rampant in two of Iraq’s main Sunni cities, overrunning police stations and sweeping through the streets, emboldened by mounting sectarian tensions between the country’s minority Sunnis and the Shiite-led government.

Troops hammered the militants with Hellfire rockets recently sent by the United States to help the government in its fight against al-Qaeda, which also operates with increasing strength in the civil war across the border in Syria. The militants’ swift uprising a day earlier overwhelmed police forces in Ramadi and Fallujah, two cities in the Sunni heartland of Anbar province that were once strongholds for militants battling U.S. troops, who pulled out of the country in late 2011.

Al-Qaeda’s Iraq branch appeared to be trying to exploit Sunni anger after authorities in the past week arrested a senior Sunni politician accused of terrorism and dismantled a months-old sit-in in Ramadi by Sunnis protesting discrimination by the government. The moves added fuel to sectarian violence that has escalated in the past year.

In violence outside Anbar, a pickup truck laden with explosives blew up on a busy commercial street Thursday evening in the city of Balad Ruz, 45 miles northeast of Baghdad, destroying several shops. At least 19 people were killed and 37 were wounded, according to security and health officials, who spoke on the condition of anonymity because they were not authorized to talk to the news media.

Al-Qaeda militants have been presenting themselves as the Sunnis’ champions against the government. Still, major Sunni tribes in Anbar and elsewhere oppose al-Qaeda and are fighting against it.

In a concession to Sunnis after the sit-in was dispersed, Prime Minister Nouri al-Maliki, a Shiite, on Wednesday pulled back military troops from Anbar, allowing local police to take over security duties. That was a main demand of discontented Sunni politicians, who see the army as a tool that Maliki uses to target his rivals and consolidate power.

But soon after the pullout, the militants launched the simultaneous assaults in Ramadi, Fallujah and at least two other nearby towns. They seized police stations and military posts, freed prisoners, and fanned out in the streets, setting up checkpoints. Some were seen cruising in captured security forces’ vehicles, waving black al-Qaeda banners.

Maliki quickly ordered military reinforcements back in.

In another apparent move to maintain Sunni support, security forces arrested a controversial Shiite cleric who leads an Iranian-­backed militia. Sunnis have long accused the government of targeting only Sunni militant groups while blessing Shiite ones.

Saad Maan Ibrahim, a spokesman for the Interior Ministry, said the cleric, Wathiq al-Batat, was arrested in Baghdad on Wednesday. The spokesman gave no details.

The cleric had been wanted by the government since last year. Batat formed the Mukhtar Army to protect Shiites from attacks by Sunni extremists. He claims to have more than 1 million members, a number that has not been independently verified.

Iraq has experienced a wave of sectarian violence since April, when security forces broke up a Sunni protest in a bloody crackdown. Since then, militant attacks have swelled, and Shiite militias have grown more active. The United Nations said Wednesday that 2013 saw Iraq’s highest annual death toll in years, since the worst of the country’s sectarian bloodletting began to subside in 2007. It reported that 7,818 civilians and 1,050 members of the security forces were killed in violence last year.

— Associated Press