TIKRIT, Iraq, Dec. 22 (Xinhua) -- Four paramilitary Sunni tribal fighters were killed and a fifth wounded Friday in an attack by gunmen in Iraq's central province of Salahudin, a provincial security source told Xinhua.

The attack occurred at dawn when unidentified gunmen opened fire on the paramilitary fighters at an outpost near the main road, some 30 km south of the provincial capital city Tikrit, the source said on condition of anonymity.

The attackers withdrew from the scene after the attack into dense orchards in the nearby bank of Tigris River, the source said.

The predominately Sunni Arab province of Salahudin has been the scene of a major offensive by Iraqi security forces and allied Hashd Shaabi units to drive out Islamic State (IS) militants from the provincial key cities and towns, including its capital city Tikrit, some 170 km north of Baghdad.

The attack also came after the Iraqi Prime Minister Haider al-Abadi on Dec. 9 officially declared full liberation of Iraq from IS militants after Iraqi forces recaptured all the areas once seized by the extremist group.

However, small groups and individuals of IS militants melted in urban areas or resorted to deserts and rugged areas in many areas in Iraq looking for safe havens. They still capable of carrying out attacks from time to time against the security forces and civilians.