BAGHDAD/BARTELLA, Iraq (Reuters) - Islamic State fighters retreating in the face of a seven-week Iraqi military assault on their Mosul stronghold have hit back in the last two days, exploiting cloudy skies which hampered U.S.-led air support and highlighting the fragile army gains.

In a series of counter-attacks since Friday night, the jihadist fighters struck elite Iraqi troops spearheading the offensive in eastern Mosul, and attacked security forces to the south and west of the city.

On Sunday two militants tried to attack army barracks in the western province of Anbar. Police and army sources said the attackers were killed before they reached the base.

Iraqi officials say they continue to gain ground against the militants who still hold about three-quarters of the country’s largest northern city.

One military source said the militants had taken back some ground, but predicted their gains would be short-lived. “We withdraw to avoid civilian losses and then regain control. They can’t hold territory for long,” the source said.

But the fierce resistance means the military’s campaign is likely to stretch well into next year as it seeks to recapture a city where the jihadists are dug in among civilians and using a network of tunnels to launch waves of attacks.

This has prompted fears among residents and aid groups of a winter food, water and fuel supply crisis for the million residents still in Islamic State-held areas of the city, and calls to speed up operations.

“Daesh (Islamic State) still controls our neighborhood, and the Iraqi forces have not taken a single step forward in three weeks. We’re in despair,” said a resident in the southeastern district of Intisar, where the army’s Ninth Armored Division has struggled to make gains.

“My family and I have been sleeping under the concrete stairs in our house for a month now, afraid of the random bombardment between the Iraqi forces and the Daesh elements,” he told Reuters by telephone.

Slideshow ( 7 images )

“PEOPLE TRAPPED”

The capture of Mosul, the largest city under control of Islamic State in Iraq and Syria, is seen as crucial towards dismantling the caliphate the militants declared over parts of the two countries in 2014.

Some 100,000 Iraqi soldiers, Kurdish security forces and mainly Shi’ite paramilitary forces are participating in the assault that began on Oct. 17, with air and ground support from a U.S.-led international military coalition.

A senior officer in the Counter Terrorism Services (CTS) said its troops battled on Sunday to clear Islamic State fighters from one eastern Mosul district, using heavy machine guns and rockets.

“Since early morning our troops have been clearing out around 40 Islamic State militants,” said Lt. Gen Abdul Wahhab al-Saidi, as heavy gunfire rattled behind him. “It’s an ongoing operation and we have killed most of the militants.”

“People are trapped in the neighborhood and some have been killed,” said one resident fleeing into an area controlled by Iraqi forces. “They threatened us to try to force us to leave with them, but we refused,” he said referring to militants.

Hundreds of residents in another neighborhood retaken from Islamic State queued for cooking gas canisters, some squabbling among themselves for a place in the line, others carting away their cylinders on their backs or in wheelbarrows and carts.

Iraqi commanders say they have killed at least 1,000 Islamic State fighters. A government adviser estimated the jihadist group now had about 4,000 fighters in Mosul.

Slideshow ( 7 images )

The military has not given figures for its own casualties. The United Nations said last week nearly 2,000 members of the Iraqi security forces were killed across Iraq in November - a figure which Baghdad says was based on unverified reports.

The elite CTS units and the armored division have captured around half of the eastern side of Mosul, which is split down the center by the Tigris river.

A U.S.-led coalition has bombed four of the five bridges across the river, aiming to stem a flow of suicide car bombers coming from the west of the city to target the army in the east.

TANKS STRUGGLE

Officers say Islamic State has deployed more than 650 car bombs, but that the pace of attacks has fallen off.

In the Intisar district, the tanks of the armored division have struggled to adapt to close-quarter urban warfare, and commanders have summoned infantry reinforcement, an officer said.

Commanders also hope to stretch Islamic State defenses more thinly, by opening new fronts inside the city.

The head of the police rapid response forces, stationed a few miles south of Mosul on the west bank of the Tigris, told Iraqi television his units were awaiting orders to advance north towards the city.

First they must take control of the Islamic State-held village of Albu Saif, the last obstacle before reaching Mosul airport on the southern edge of the city.

A military statement said the army had captured on Sunday three villages near the town of Shirqat, further south from Mosul and close to the sites of two attacks on Friday night by Islamic State fighters which killed 12 people.