KIRKUK, Iraq, Dec. 24 (Xinhua) -- Five people including a police officer were killed Sunday in an ambush by Islamic State (IS) militants in Iraq's northern province of Kirkuk, a police source told Xinhua.

The incident took place when IS militants set up a fake checkpoint on a road connecting the town of Ryadh and Hawijah in southwestern part of Kirkuk province, and intercepted a car carrying the five people, including Colonel Fadhel al-Sab'awi head of a police station, and shot them dead, the source from Kirkuk police said.

The extremist militants fled the scene after killing the five people, the source said, adding that the security forces launched a search campaign searching for the attackers.

Earlier in the day, a security source from the neighboring Salahudin province told Xinhua that four paramilitary Hashd Shaabi members were killed and six others injured in an attack by more than 30 IS militants on a Hashd Shaabi base near the town of Dour in east of the provincial capital Tikrit, some 170 km north of Baghdad.

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 are still capable of carrying out attacks from time to time against the security forces and civilians.