Hundreds of Mosul residents fled liberated areas of the city on Sunday after Islamic State sleeper cells attacked Iraqi forces and burned houses, highlighting the precarious security situation.
Iraqi forces fought with militants in the al-Tanak and Yarmouk neighbourhoods in the western side of the city, which had been retaken several weeks ago.
The Islamic State of Iraq and the Levant (Isil) jihadists set fire to a number of houses and cars in the area before launching suicide attacks.
Footage showed families, fearing a return to Isil rule, leaving by car and on foot against a backdrop of rising black smoke.
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A top commander in the Counter-Terrorism Service (CTS), which sent forces to fight the Isil gunmen, said the attackers had infiltrated the area by blending in with returning displaced civilians.
"The group came with the displaced and settled in the Tanak district. They regrouped and launched counterattacks," Staff Lieutenant General Abdulwahab al-Saadi said.
More than 15 Isil fighters were killed, as well as several civilians, in the battle.
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"Yarmuk is being searched house to house," Gen Saadi said, adding that two groups of Isil attackers were still believed to be in the area, which lies on the western edge of the city.
There were also reports Iraqi intelligence officers carried out night raids on a refugee camp south of Mosul, seizing a number of weapons.
“The plan by Isil sleeper cells and sympathisers was to take control of the camp and turn it into hostage situation," one intelligence officer said.
While thousands of men and teenage boys have been detained and questioned on suspicion of links to the jihadist group, it has proved difficult to completely root out all sympathisers and sleeper cell members.
The east bank of Mosul, a city divided by the Tigris River, was retaken in January and a push to wrest back the western side was launched in mid-February.
More than 800,000 people have been displaced from the Mosul area since October last year and the security forces are struggling to carry out effective screening.
While the exact circumstances were unclear, Sunday night's attack was described as a diversionary tactic by west Mosul cells to ease the pressure on the Old City, where the jihadists appear to be on their last legs.
Iraqi forces, led by the CTS, have for a week been pressing a perilous assault into the Old City in central Mosul, the last pocket still controlled by the jihadists.
The forces are having to go street-to-street with little protection or heavy weaponry through the ancient part of the city’s narrow streets.
In its last throes, Isil’s estimated 300 remaining fighters have been targeting troops with snipers and suicide bombers hidden among fleeing residents.
Three journalists, one Iraqi Kurdish and two French, were killed last week after the group set off an IED.