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.

raqi officials say they continue to gain ground against the militants who still hold about three-quarters of the country's largest northern city which is Islamic State's last major urban stronghold in Iraq.

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.

Read more:  Reuters