Three policemen were killed in a bomb attack on their patrol on Tuesday in Mosul, the capital of Nineveh province in northern Iraq, a provincial police source said.

An unknown gunman hurled hand grenades on a police patrol in the Wadi Egab neighborhood in southern Mosul, damaging a police vehicle and killing three policemen aboard, the source told Xinhua on condition of anonymity.

The attacker fled the scene after the attack, the source said.

Meanwhile, the source said that an earlier twin bombing that badly damaged a church in the al-Shifaa neighborhood in northwestern Mosul, were carried out by a booby-trapped cart and followed by a roadside bomb explosion.

Earlier in the day, the source said the double attacks were carried out by two car bombs.

He said the first blast caused serious damages to the church building, and ten minutes later the second blast hit Iraqi security forces arriving to the scene and dozens of onlookers gathered near the church building, killing five people and wounding 40 others.

Islamic extremists have frequently targeted Christians since the U.S.-led invasion in 2003, forcing tens of thousands to flee Iraq.

Iraq's Christian community has been estimated at 3 percent of Iraq's roughly 30 million people, and has a significant presence in the Nineveh province, which has been the scene of major security crackdowns by U.S. troops and Iraqi security forces to uproot the insurgency that erupted shortly after the U.S.-led invasion.