A suicide truck bomber attacked a police station in one of Iraq's major oil hubs on Saturday, killing at least seven people and injuring 13 in a neighborhood home to many refinery workers and engineers, police said. The attack in Beiji was at least the third deadly suicide attack in 24 hours in Iraq and came a day after a key oil pipeline in the northern city was struck by an insurgent bomb. The bomber on Saturday approached the police station in an explosives-laden truck about five kilometers north of the city center, a police official said, speaking on condition of anonymity because he was not authorized to release details of the attack. The official said five policemen and two civilians were killed in the blast, which damaged nearby homes and sent shards of glass flying through the air. "The windows of my house shattered and three of my family members were injured," said Jassim Salih, who lives nearby. Another witness, Falih Salim, said he rushed toward the area after hearing the explosion and saw the bodies of two burned guards. "The scene was so horrible that I ran away." Salim said. Beiji, 250 kilometers north of Baghdad, houses northern Iraq's largest oil refinery, and serves as a key transfer point for crude oil being exported out of Iraq. Attacks on the Kirkuk-Beiji pipeline cluster have been infrequent in recent months, with some 300 US soldiers and more than 2,000 Iraqi troops guarding the zone. Violence is generally down throughout Iraq, largely due to the influx of US troops that began last February, the rise of the anti-al-Qaida groups and a freeze on activities by the Mahdi Army, ordered by the militia's leader, the radical cleric Muqtada al-Sadr. But with the lost of many former sanctuaries, al-Qaida groups are believed to be moving northward. On Wednesday, US military commanders told visiting US Defense Secretary Robert Gates that they need more troops to confront al-Qaida fighters who have been pushed out of the Baghdad region. The two suicide attacks on Friday were the latest in a series of al-Qaida assaults against US-backed Sunni groups that have turned against the organization. In one, in Muqdadiyah, a woman detonated explosives in front of the building housing the office of the 1920 Revolution Brigade, a Sunni insurgent group whose members in the area switched sides this year and joined the fight against al-Qaida. Police chief Brig. Gen. Mohammed al-Tamimi said 15 people were killed and 20 wounded. US officials put the toll at 12 dead and 17 wounded. Later Friday, a suicide car bomber struck at a checkpoint about 15 kilometers away, killing seven Iraqi soldiers and three members of a local anti-al-Qaida group, Iraqi army Capt. Saad al-Zuhairi said. Al-Zuhairi, who was about 150 meters away, said the driver detonated his explosives when the guards asked to search the car. Ibrahim Bajalan, the head of the Diyala provincial council, said the female bomber was a former member of Saddam Hussein's Baath Party whose two sons joined al-Qaida and were killed by Iraqi security forces. "She wanted to avenge the killing of her two sons," he told The Associated Press, quoting what he said were reports from officials at the scene. Jassim Jerad, a former Iraqi soldier who was injured in the Muqdadiyah bombing, said he saw a woman approaching the offices, then felt the force of the blast. "I fell down, but stood up quickly to save my son, who was screaming," he said from his hospital bed, while his 6-year-old son wept nearby. Kuudur Alwan, a member of the anti-al-Qaida group, said he was buying groceries near the targeted building when he suddenly felt "heat hitting my chest and right leg." "I limped toward the building to see several of my awakening colleagues dead and their bodies left on the ground," he said from his hospital bed in Jaluala. American commanders are working with nearly 60,000 volunteers in the awakening groups to help provide security in wide areas of Iraq, including Diyala province, a farming and industrial region that extends from the suburbs of Baghdad to the Iranian border. Diyala had been an al-Qaida stronghold from 2006 until last summer, when US and Iraqi soldiers drove extremists from the provincial capital of Baqouba, which the terror movement had declared the capital of the Islamic State of Iraq.