By Ahmed Aboulenein and Ahmed Rasheed

SOUTHWEST OF MOSUL, Iraq/BAGHDAD (Reuters) – The U.S.-backed Iraqi offensive to take back Mosul from Islamic State gained fresh momentum on Thursday, with an armored division trying to advance into the city from the northern side.

The militants are now besieged in the northwestern corner of Mosul which includes the historic Old City center, the medieval Grand al-Nuri Mosque, and its landmark leaning minaret where their black flag has been flying since June 2014.

The Iraqi army’s 9th Armoured Division and the Rapid Response units of the Interior Ministry have opened a new front in the northwest of the city, the military said in a statement.

The attack will help the elite Counter-Terrorism Service (CTS) and Interior Ministry Federal Police troops who are painstakingly advancing from the south.

“Our forces are making a steady advance in the first hours of the offensive and Daesh fighters are breaking and retreating,” Brigadier General Yahya Rasool, a spokesman for the joint operations command, told state television. He was referring to Islamic State by an Arabic acronym.

Federal Police and Rapid Response forces advanced 1,400 meters and keep pushing ahead in the Hulela area toward the Haramat district northwest of Mosul. They were trying to reach the Tigris river bank and surround the Fifth Bridge north of the Old City, the Federal Police said in a statement.

A U.S.-led international coalition is providing key air and ground support to the offensive on Mosul, Islamic State’s de facto capital in Iraq, which started in October.

It was from the pulpit of the Grand al-Nuri Mosque that Islamic State leader Abu Bakr al-Baghdadi revealed himself to the world in July 2014, declaring a “caliphate” that spanned parts of Syria and persecuted non-Sunni communities as well as Sunnis who did not abide by its extreme interpretation of Islam.

“An armored division should not be going into narrow alleyways and streets but we will,” said Lieutenant General Qassem al-Maliki, commander of the 9th Armoured Division.

“There are sometimes troop shortages or orders that require us to do so and we will do our duty,” he told Reuters in an interview at a base southwest of Mosul.

“We will enter with Rapid Response forces and CTS and we will enter as one front.”

The Iraqi army said on April 30 that it aimed to finish the battle for Mosul, the largest city to have fallen under Islamic State control in both Iraq and Syria, this month.

Islamic State’s defeat in Mosul will not mean the end of the hardline Sunni group which remains in control of parts of Syria and vast swathes of Iraqi territory near the Syrian border.

SHAPING THE BATTLEFIELD

Close U.S. support should help the involvement of the armored division and reduce the risk for civilians, U.S. Army Lieutenant Colonel James Browning, the partnered advisor to the Iraqi 9th Armoured Division, told Reuters at the base.

“Everything I am trying to do is try to shape the battlefield for him,” Browning, a battalion commander from the 82nd Airborne Division, said referring to Maliki.

“I am looking at trying to strike right in front of him as well as deep, even into Old Mosul.”

U.S. support is essential for getting rid of suicide car bombs, known as VBIEDs, driven by the militants as road torpedoes before crashing into troops.

A typical conversation between Browning and Maliki would go like this: “What are you seeing on the screen? Do you see civilians?” Browning recalls Maliki asking.

“And sometimes I say ‘yes’ and he (Maliki) says ‘don’t strike’. I go through that process every time. We scan, we take a look, we make sure,” Browning said.

The war is taking a heavy toll on civilians trapped behind Islamic State lines and used by the militants as shields.

Local officials and eyewitnesses have said as many as 240 people may have died in March in the Al-Jadida district of western Mosul when a blast resulted in a building collapsing.

The U.S. military has acknowledged that the U.S.-led coalition probably had a role in the March 17 explosion, but said Islamic State also could be to blame.

(Reporting by Ahmed Aboulenein southwest of Mosul and Ahmed Rasheed in Baghdad; Additional reporting by Isabel Coles in Erbil; Writing by Maher Chmaytelli; Editing by Ralph Boulton)