Twelve members of a family were shot dead by unknown gunmen in Iraq's central province of Salahudin, a provincial police source told Xinhua.

The incident took place on Saturday early morning when unidentified gunmen broke into a house of a family and shot dead 12 members in Farhatiyah area near the town of Balad, some 80 km north of the Iraqi capital Baghdad, the source said on condition of anonymity.

Only a six-month infant survived the attack, despite receiving a bullet in his body, the source said.

The Sunni Arab family has just returned home at the rural area of Farhatiyah after being displaced for four years, the source said, adding that the area is under control of paramilitary Hashd Shaabi forces and a police force.

Iraqi security forces arrived in the morning and launched an investigation into the incident, fearing that the attack was part of sectarian strife that engulfed Iraq after the U.S.-led invasion in 2003, the source added.

Salahudin province was reported the scene of another attack in the morning when roadside bomb struck a police patrol at a village near the city of Shirqat, some 280 km north of the Iraqi capital Baghdad, destroying a police vehicle and killing four policemen aboard.

The key cities of Salahudin province, including the provincial capital Tikrit, some 170 km north of Baghdad, was captured by Islamic State (IS) militants in June 2014, but the Iraqi security forces freed the province during major anti-IS offensives.