Iraqi special forces recaptured six districts of eastern Mosul on Friday, a military statement said, expanding the army’s foothold in the Islamic State bastion a day after its leader told his jihadist followers there could be no retreat.

An officer in the elite Counter Terrorism Service, which has spearheaded the Mosul offensive, said its troops had launched a major operation against the militants who are now almost surrounded in their last major urban redoubt in Iraq.

CTS special forces took over the neighborhoods of Malayeen, Samah, Khadra, Karkukli, Quds and Karama, the statement said, inflicting heavy losses on the militant fighters and raising the Iraqi flag over buildings. One Mosul resident, speaking to Reuters by phone, said he could still hear the sound of fighting coming from one of those districts.

The territory taken by the government still amounts to just a fraction of the sprawling city, which is divided into dozens of residential and industrial districts and held 2 million people before it was captured by Islamic State in 2014.

The battle to drive the fighters out is the biggest ground operation in Iraq since the U.S.-led invasion in 2003, and is likely to decide the fate of the self-proclaimed Islamic State caliphate that has defied the world for two years.

The advances took the troops 1 mile (1 1/2 km) inside the city. Districts captured so far, however, are less built-up than other areas, particularly those on the west bank of the Tigris River, where the population is more exclusively Sunni Muslim Arab and the hardline Sunni Islamists could be more deeply embedded.

Iraqi officers and those from a U.S.-led coalition providing air and ground support to the offensive say progress has been faster than expected, but stress that the operation is still in its early stages.

Speaking at the CTS command post in the village of Bartella, east of Mosul, a senior officer said the advancing troops were coming up against fierce opposition, including car bombs and sniper fire.

In the village of Ali Rash, 7 km (4 miles) to the south east, a Reuters reporter heard helicopter gunships and cannon fire over Mosul. Volleys of automatic rifle fire, possibly from the militants, were also audible and smoke could be seen rising from the east of the city.

An officer in the village said Iraqi troops had also taken two thirds of another Mosul district, Intisar, in the same eastern section of the city.

Islamic State fighters “are trying to get away”, Lieutenant-General Qassem Jassim Nazzal told Reuters.

In a sign of the fierce resistance which soldiers have encountered since entering the city on Monday, Nazzal said they blew up six bomb-laden cars, killed two suicide bombers, and killed 30 other people.

In the village of Ali Rash, retaken by Iraqi forces sweeping toward Mosul from the south and the east, the bloated and blackened bodies of three Islamic State fighters, dressed in khaki trousers and military boots, were left out in the open.

“They’re criminals, let the dogs eat them,” another officer said.

SPECIAL FORCES

Iraqi regular troops and special forces, Shi’ite militias, Kurdish peshmerga fighters and other groups backed by U.S.-led air strikes launched their campaign to retake Mosul nearly three weeks ago.

Winning back the city would crush the Iraqi half of a cross-border caliphate declared by Islamic State leader Abu Bakr al-Baghdadi from a Mosul mosque two years ago.

Islamic State also holds large parts of neighboring Syria, but Mosul is by far the largest city under control of the ultra-hardline militants in either country, many times bigger than any other city the militants have held.

In a speech released on Thursday Baghdadi - whose whereabouts are unknown - said there could be no retreat in a “total war” against the forces arrayed against Islamic State, telling fighters they must remain loyal to their commanders.

Mosul 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. Iraqi officials say Islamic State is holding the civilian population as human shields.

U.N. human rights spokeswoman Ravina Shamdasani said on Friday Islamic State fighters had killed hundreds of people, including 50 deserters and 180 former Iraqi government employees, around Mosul.

They have also transported 1,600 people from the town of Hammam al-Alil, south of Mosul, to Tal Afar to the west, possibly for use as human shields against air strikes, and told residents to hand over boys above the age of nine, in an apparent recruitment drive for child soldiers.

The United Nations says 22,000 people have been displaced since the start of the Mosul campaign, not including thousands from outlying villages forced to head to Mosul by retreating Islamic State fighters who used them as human shields.

ROCKET LAUNCHERS

Mosul residents, speaking to Reuters by telephone, said Islamic State fighters were deploying artillery and rocket launchers in 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 airport, they said.

“We saw Daesh (Islamic State) fighters installing a heavy anti-aircraft machine gun alongside a rocket launchpad, and mortars as well,” one Mosul resident said.

People in southern and eastern neighborhoods reported on Thursday night that their houses had been shaken by artillery and rocket barrages launched from their districts toward the advancing troops.

As well as the Islamic State resistance in Mosul itself, the militants have launched diversionary attacks across the country since the start of the offensive.

In the town of Shirqat, about 100 km (60 miles) 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 bank of the Tigris into the town at 3 a.m., taking over al-Baaja mosque and fanning out into alleyways. Security forces imposed a curfew and said reinforcements from the Popular Mobilisation, or Hashid Shaabi, forces were being sent to the town.

In their drive toward Mosul, Iraqi troops and Kurdish peshmerga fighters have closed in from the north, from the eastern Nineveh plains and up the Tigris from the south.

The Hashid Shaabi forces of mainly Shi’ite militias joined the campaign on Saturday, launching an offensive to cut off the west.

A Hashid spokesman said they had made progress but had not completely closed off the western flank, and their fighters had seen some cars leaving Mosul on Thursday.