Baghdad, June 4 (IANS): Iraqi security forces on Thursday repelled multiple suicide car bomb attacks by Islamic State (IS) militants, while clashes with the extremist group continued in the provinces of Salahudin and Anbar, a security source said.

In Iraq's northern central province of Salahudin, the security forces and allied militias, known as Hashd Shaabi (Popular Mobilization), shot dead four suicide bombers wearing explosive vests when they tried to approach the troops' positions in Fat'ha area east of the IS-held town of Baiji, some 200 km north of Iraq's capital Baghdad, a provincial security source told Xinhua news agency.

Meanwhile, the troops continued their heavy clashes with IS militants at the edge of Baiji, but their advance was slowed down by sporadic suicide bomb attacks, the source said.

The troops have attacked Baiji from several directions and managed to free the industrial district just outside the town, while tit-for-tat battles continued between the IS militants and the security forces on the bank of the Tigris river east of Baiji, the source said.

In addition, the troops and Hashd Shaabi fighters clashed with the extremist militants in Iraq's largest oil refinery, just north of Baiji, most of which is under IS control, the source added.

The battles in Baiji and the nearby oil refinery came four days after the town's mayor, Mohammed Hammed, told Xinhua that the troops freed several villages outside the town and were preparing to recapture it.

Also in the province, the security forces and allied militias halted their offensive launched on Wednesday west of the city of Samarra, some 120 km north of Baghdad, after the troops faced fierce resistance by the militants, the source said.

The offensive west of Samarra was designed to secure the vast area and to recapture the strategic desert roads leading to the militant-seized city of Fallujah in the neighbouring Anbar province.

Since March 2, thousands of allied Shia and Sunni militias have been involved in Iraq's biggest offensive to recapture the northern part of Salahudin province, including Tikrit and other key towns and villages, from IS militants.

In Anbar province, Iraqi soldiers repelled two suicide attacks by two military Humvees packed with explosives on an army base near Tharthar Lake east of Fallujah, some 50 km west of Baghdad, a provincial security source told Xinhua.

The first booby-trapped Humvee went off near the outer defence line, leaving two soldiers dead and six wounded, but the second attacker was hit by an anti-tank guided missile before reaching his target, the source said.

Separately, the IS militants attacked military bases in the desert area north of Fallujah, killing 17 soldiers and Hashd Shaabi fighters and injuring eight, the source said.

Four soldiers were killed and nine wounded in a mortar barrage by the IS militants on al-Mazraa army camp east of Fallujah, the source said.

Also in the province, six government-backed Sahwa Sunni paramilitary fighters were killed and four wounded in a mortar barrage on their base in the town of Barwana near the city of Haditha, some 200 km northwest of Baghdad, the source added.

In Baghdad, a booby-trapped car detonated in the industrial area in Baiyaa district in the southern part of the capital, leaving two people dead and seven injured, an interior ministry source told Xinhua.

The security situation in Iraq deteriorated drastically since June last year, when bloody clashes broke out between Iraqi security forces and IS militants.