Battle for Mosul: US troops fighting near front lines as Iraqi offensive slows

US soldiers have moved into Mosul and are now operating near constantly shifting front lines amid fierce house-to-house fighting and car bomb attacks, the Pentagon said, as months of Iraqi operations to defeat the Islamic State group grind on.

Colonel John Dorrian, a spokesman for the US-led coalition against IS, said on Wednesday that special forces, intelligence and engineering troops were closely involved with Iraqi attempts to retake Iraq's second city. 

“They have been in the city at different times, yes," said Dorrian. "They've advised the Iraqi security forces as they've moved forward."

Dorrian added that his troops "remain behind the forward line” - but also said that line was constantly shifting amid "room-to-room" fighting and urban warfare marked by constant attacks from car bombs (see video below).

"There are more than 200,000 buildings in Mosul. You end up having to clear each one," he said. "That means going through every single room and every single closet. It's going to take time. It's going to be very dangerous."

MORE: Why Mosul, world's biggest military operation, has run into trouble

Dorrian said US and coalition advisers involved in retaking the city had doubled to 450 in recent weeks.

He declined to say whether the Iraqi advance was proceeding according to schedule, amid reports that the efforts had slowed in the face of fierce resistance by IS and mounting casualties among Iraqi troops.

Dorrian's comments come as the IS group released drone footage of attacks on Iraqi forces inside Mosul.

The video shows cars rolling down streets before reaching their targets in the east of the city. Huge blasts then erupt from the vehicles, destroying almost everything around them.

IS has used hundreds of car bombs in the battle for Mosul. Many vehicles used are armoured, making it difficult to impossible for Iraqi forces to destroy them before they reach their targets.

READ: How IS has made life tough for Iraq's elite forces in Mosul

The UN said in December that more than 2,000 Iraqi soldiers had been killed since the launch of the Mosul offensive in October.

In December, one senior Pentagon official told Politico that some Iraqi battalions were suffering up to 50 percent casualty rates.

The US has approximately 5,000 troops in Iraq, many of whom are stationed away from combat.

Offensive in western Iraq

Iraqi forces on Thursday announced they had launched an offensive to retake towns still under the control of IS in western areas near the border with Syria, commanders said.

"A military operation has begun in the western areas of Anbar to liberate them from Daesh," said Lieutenant General Qassem Mohammedi, of the Jazeera Operations Command, using an Arabic acronym for IS.

'Zero hour has come to liberate the western areas'

- Nadhom al-Jughaifi, commander with Haditha tribal fighters

The militants' hub of Al-Qaim, which lies 330km northwest of Baghdad, is still a long way down the road and the most immediate target of the new offensive is the town of Aanah.

"Our forces started advancing from Haditha towards Aanah from several directions," Mohammedi told AFP.

Haditha was never seized by IS when the group swept across much of Iraq's Sunni Arab heartland in 2014 and is home to a tribe that has led the fight against the group in the area.

"Zero hour has come to liberate the western areas," Nadhom al-Jughaifi, a commander with the Haditha tribal fighters, said.

He said the operation was led by the army's 7th division, police, and fighters from local tribes that have opposed the militants, with aerial backing from the US-led coalition.

The main targets of the operation are Aanah, Rawa and Al-Qaim, the westernmost Iraqi towns along the Euphrates valley.

Meanwhile, a surge in violence across Baghdad continued, as two car bombs claimed by Islamic State group killed at least 14 people on Thursday.

The first blast shook Baghdad's eastern al-Obeidi area during the morning rush, killing six and wounding 15. IS said in an online statement it had targeted a gathering of Shia Muslims, whom it considers apostates.

The second explosion hit the central district of Bab al-Moadham near a security checkpoint, killing eight. Both bombs had been left in parked vehicles.