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RAMADI, Iraq, May 31 (Xinhua) -- Iraqi security forces on Tuesday repelled an attack by Islamic State (IS) militants in south of the IS-held city of Fallujah in Iraq's western province of Anbar, leaving at least 32 IS militants killed, a security source said.

Dozens of IS militants at dawn attacked the positions of the security forces in Nuaimiyah area in southern Fallujah, some 50 km west of the Iraqi capital of Baghdad, the source told Xinhua on condition of anonymity.

Some of the IS militants used tunnels dug earlier by them and a number of snipers deployed in the area when they attacked the military positions, but the troops backed by U.S.-led and Iraqi aircraft repelled the attack, killing at least 32 militants and destroying eight of their vehicles, including six car bombs, the source said without giving further details about casualties among the security forces.

Nuaimiyah is agricultural area extending from the southern part of Fallujah. It was the scene of fierce clashes on Monday after the security forces pushed into it and managed to capture a foothold into its farms.

Meanwhile, the security forces and allied paramilitary Shiite and Sunni units, known as Hashd Shaabi, continued their battles around the IS-held town of Saqlawiyah in northwest of Fallujah, in an attempt to free the town from IS militants, the source said.

During the day, battles around Fallujah continued as the troops faced fierce resistance from the extremist militants inside the city, the source said, adding that the advance is expected to be slow as the security forces have orders to spare the lives of tens of thousands of civilians trapped inside Fallujah, in addition to hundreds of hidden bombs are believed to be planted by the militants to hamper the advance of the troops.

Earlier, Brigadier General Yahya Rasoul, spokesman for the Joint Military Command, said that intelligence reports indicate that about 400 to 600 militants are in Fallujah, many of them foreigners. He said about 50,000 to 70,000 civilians are expected to remain in Fallujah.

Monday operation to free Fallujah and nearby areas came a day after the security forces said that they have completed preparation for final attack to retake the IS-held city of Fallujah.

On May 23, Iraqi Prime Minister Haider al-Abadi announced the launch of the offensive to claim Fallujah, during a time in which the country is struggling in a chaos to reshuffle the cabinet.

Government troops and allied militias have currently been fighting for months to reclaim key cities and towns in Anbar from IS militants, who attempted to advance towards Baghdad after seizing most of Anbar province.

Also on Tuesday, up to five people were killed and 17 others wounded in two suicide bomb attacks targeting Hashd Shaabi unit members in Iraq's Salahudin province, a provincial security source told Xinhua.

The first explosion occurred around noon when a suicide bomber rammed his explosive-laden car into a checkpoint manned by members of Hashd Shaabi unit at the entrance of the town of Sulaiman Beg, some 90 km east of the provincial capital city of Tikrit, the source said.

Minutes later, another suicide bomber wearing explosive vest blew himself up when security forces and people gathered at the site of the first blast, the source added.

Earlier, the source put the toll at four people killed and 11 wounded by the double suicide bomb attacks.

The attackers apparently followed a familiar tactic frequently used by insurgent groups which depends on creating an initial explosion to attract security forces and people, then they set off another blast to get heavier casualties, according to the source.

Nor group has so far claimed the attacks in Sulaiman Beg, but the IS group frequently carried out massive attacks against civilians and military across the country in an attempt to distract the security forces' attention away from the front lines.

A report by the UN Assistance Mission for Iraq estimated that 741 Iraqis were killed and 1,374 others wounded in acts of terrorism, violence and armed conflicts in April across Iraq.