TIKRIT, Iraq, Dec. 24 (Xinhua) -- Iraqi security forces Sunday launched an operation to clear Himreen mountainous area from Islamic State (IS) militants in Iraq's central province of Salahudin, a police source said.

The Iraqi forces, backed by helicopter gunships, cleared large areas in Himreen mountain range in the northeastern part of the province and seized a number of IS hideouts containing weapons, ammunition and military equipment, the source told Xinhua on condition of anonymity.

The helicopters pounded some IS posts on high mountains and trenches in the rugged area of Himreen mountain range, which represents the provincial border line between Salahudin and Kirkuk provinces, the source said.

The troops killed at least seven IS militants, while five security members, including a police officer, were wounded during the operation, the source added.

Earlier in the day, a provincial security source told Xinhua that four paramilitary Hashd Shaabi members were killed and six others injured when more than 30 IS militants riding ten vehicles carried out an overnight attack on a Hashd Shaabi base near the town of Dour in east of the provincial capital Tikrit, some 170 km north of Baghdad.

The IS militants came from the rugged area that extends to IS redoubt in Mteibijah area in the eastern part of Salahudin province, according to the security source.

The extremist militants waged the attack from the rugged area despite an operation on Dec. 16, when the Iraqi forces swept the eastern part of the province to hunt down remnants of IS militants.

The sprawling rugged area also extends to the western part of neighboring Diyala province and the nearby Himreen mountainous area in northeastern Salahudin province.

During the past few months, dozens of IS militants fled their former bases in Salahudin province and Hawijah area in west of Kirkuk after the Iraqi forces cleared these areas during major anti-IS offensives.

On Dec. 9, Iraqi Prime Minister Haider al-Abadi 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.