BAGHDAD, Aug. 26 (Xinhua) -- Four Islamic State (IS) militants were killed Sunday in an ambush by paramilitary Hashd Shaabi fighters at a rugged area in Iraq's central province of Salahudin, a Hashd Shaabi source said.

The incident took place in the evening when Hashd Shaabi fighters ambushed a group of IS militants who were trying to infiltrate from IS hotbed of Mteibijah, a rugged area in the eastern part of the province, to nearby villages, Khudhair al-Matrouhi, leader of a Hashd Shaabi unit, told Xinhua.

As the militants entered the ambush area, the troops opened heavy fire on them and killed four militants while the others fled the scene leaving their weapons and ammunition, Matrouhi said.

Iraqi security forces repeatedly tried to retake control of Mteibijah, but the vast rugged land and mountains have made it difficult for them to dislodge the extremist militants from the region.

Hundreds of IS militants earlier fled their former bases in the key cities of Salahudin, including the provincial capital Tikrit, some 170 km north of Baghdad, after the Iraqi forces cleared these areas during major anti-IS offensives.

Late in 2017, Iraqi Prime Minister Haider al-Abadi, also the commander-in-chief of Iraqi forces, officially declared full liberation of Iraq from IS militants after Iraqi forces recaptured all the areas once seized by the extremist group.

However, some IS remnants have since melted in urban areas or fled to deserts and rugged areas in the country, carrying out attacks from time to time against security forces and civilians.