At least four people were killed in car bomb attacks in northern Iraq on Sunday, police said. In one attack, a suicide bomber rammed his explosive-laden car into the entrance of a police headquarters in the town of al- Riyadh located in west of the city of Kirkuk, some 250 km north of the Iraqi capital of Baghdad, killing three policemen and wounding 14 others with the police chief of the headquarters included, a local police source told Xinhua on condition of anonymity. In a separate incident, two car bombs went off in a quick succession at a residential Shiite Turkoman area in the city of Tuz-Khurmato, some 200 km north of Baghdad, killing one person and wounding 27, a local police source anonymously told Xinhua. The two cities are part of the disputed areas between the Kurds and both Arabs and Turkomans, which the Kurds want to incorporate into their domain. The Kurds move is fiercely opposed by the Baghdad government. Violence and sporadic high-profile bomb attacks are still common in the Iraqi cities despite the dramatic decrease in violence since its peak in 2006 and 2007, when the country was engulfed in sectarian killings.