BAGHDAD/ERBIL, Iraq (REUTERS) - Iraqi special forces stepped up attacks against Islamic State in Iraq and Syria (ISIS) fighters in their Mosul stronghold on Friday (Nov 4), seeking to expand the army's foothold in the east of the city after the leader of the terrorist group told his fighters there could be no retreat.
An officer in the elite Counter Terrorism Service said CTS troops had launched a major operation.
He gave no details, but officers have said troops fought in at least four neighbourhoods in the east of the city on Thursday (Nov 3), and may try to push all the way to the Tigris river, which runs through the centre of Mosul.
Iraqi television footage from the east of the city showed heavy palls of grey smoke rising into the sky.
Iraqi regular troops and special forces, Shi'ite militias, Kurdish peshmerga fighters and other groups backed by US-led air strikes launched a campaign two weeks ago to retake Mosul.
Winning back the city would crush the Iraqi half of a cross-border caliphate declared by ISIS leader Abu Bakr al-Baghdadi from the pulpit of a Mosul mosque two years ago.
ISIS also holds large parts of neighbouring Syria, but Mosul is by far the largest city under control of the ultra-hardline militants in either country, and the campaign to retake it is the most complex in Iraq since the 2003 US-led invasion which toppled Saddam Hussein and unleashed a decade of turmoil.
In a rare speech released on Thursday (Nov 3), Baghdadi - whose whereabouts are unknown - said there could be no retreat in a "total war" against the forces arrayed against ISIS, telling fighters they must remain loyal to their commanders.
The city is still home to nearly 1.5 million people, who risk being caught up in brutal urban warfare. The United Nations has warned of a potential humanitarian crisis and a refugee exodus, although Iraqi officials say ISIS is holding the civilian population as human shields.
Mosul residents said ISIS fighters were deploying artillery and rocket launchers inside and near residential areas.
Some were hidden in trees near the Wahda district in the south, while others were deployed on the rooftops of houses taken over by the militants in the Ghizlani district close to Mosul's airport, they said.
"We saw Daesh (ISIS) fighters installing a heavy anti-aircraft machine gun alongside a rocket launchpad, and mortars as well," one Mosul resident said.
People in the southern and eastern neighbourhoods reported on Thursday night that barrages of artillery shells and rockets being launched from their districts towards the advancing troops had shaken their houses.
As well as the ISIS resistance in Mosul itself, the militants have launched a series of diversionary attacks across the country since the start of the offensive.
In the town of Shirqat, about 100km south of Mosul, militants stormed a mosque and several houses early on Friday, a local police officer said, killing seven soldiers and fighters from the Shi'ite Popular Mobilisation force.
The insurgents crossed from the eastern side of the Tigris river into the town at 3am, taking over al-Baaja mosque and spreading out into alleyways. Security forces declared a curfew and said reinforcements from the Popular Mobilisation, or Hashid Shaabi, forces were being sent to the town.
Iraqi troops and Kurdish peshmerga fighters have closed in on it for two weeks from the north, from the eastern Nineveh plains and up the River Tigris from the south.
The Hashid Shaabi forces of mainly Shi'ite militias joined the campaign on Saturday (Oct 29), launching an offensive to cut off any supply or escape to the west.
A Hashid spokesman said they had made progress but had not completely closed off the western flank, and their fighters had seen from a distance some cars leaving Mosul on Thursday.