AKIPRESS.COM - Islamic State fighters launched a counter-attack against advancing U.S.-backed Iraqi forces in western Mosul during an overnight rain storm, as the battle for control of the militants' last major urban stronghold in Iraq intensified, Reutersreported.

Explosions and gun fire rang out across the city's southwestern districts in the early hours of Thursday. The fighting eased in the late morning, although a Reuters correspondent saw an air strike and rebel mortar fire.

A senior Iraqi officer said Islamic State staged its attack on units from the elite Counter Terrorism Service (CTS) when the storm and strong winds hampered air surveillance and on-the-ground visibility.

He said some militant fighters hid among displaced families to get close to the U.S.-trained troops.

Iraqi forces captured the eastern side of Mosul in January after 100 days of fighting and launched their attack on the districts that lie west of the Tigris river on Feb. 19.

Defeating Islamic State in Mosul would crush the Iraqi wing of the caliphate declared by the group's leader, Abu Bakr al-Baghdadi, in 2014, from Mosul's grand old Nuri mosque.

Residents reported that civilians were killed in an air strike on an Islamic State-run mosque on Wednesday, highlighting the perilous situation facing hundreds of thousands of Mosul residents as the allied forces step up their campaign.

The residents said the blast collapsed or damaged a number of neighboring houses, many of which are badly made and poorly maintained. A spokesman for the U.S.-led coalition said he was not aware of an air strike on the Omar al-Aswad mosque.

The mosque was where Islamic State sent members of the Iraqi national police and armed forces to surrender their weapons and register in a militant database when the group seized control of the city in 2014. In return they received a pass to prevent their arrest and possible execution at militant check points.