TEHRAN (Press Shia) – The Iraqi Air Force dropped thousands of leaflets over Mosul on Saturday night to warn residents of a looming offensive on the Daesh-held city.

"It's victory time," blares a headline on the newspaper-style leaflets, quoting Iraqi President Haider al-Abadi in remarks directed at Mosul's residents. "Time to celebrate a clean Iraq without Daesh or any dark belief."

Another headline reads, "We are preparing to take action to free Mosul and regain security and stability in the region."

The four-page leaflets tell residents that coalition forces are making advances on Iraq's second-largest city and that no one should panic. Residents are asked to stay away from certain parts of the city, avoid Daesh positions, remain in their homes and seal their windows and doors. A phone number for Mosul residents to report Daesh activity is included.

Iraq's Joint Military Operations said in a statement that thousands of leaflets rained down on the city center of Mosul on Saturday night.

"The newspapers have important information, to update them with the latest facts and victories," the statement said.

Residents have had limited access to the outside world since Mosul fell into the hands of the terrorist group in June 2014. Daesh imposed extreme restrictions on travel in and out of the city.

The warning to residents came hours after Deash started telling wounded fighters in Mosul that they can go to the group's power base in Syria as Iraqi forces and others prepare to retake the key city, a source inside Mosul told CNN.

The Iraqi military, Kurdish Peshmerga and a paramilitary force are getting ready for a battle expected to take place in the air and on the ground.

Daesh is releasing some low-level prisoners, the source said, such as those jailed for their beards, cigarettes or clothing offenses. Wounded Daesh fighters have been told to go to Raqqa, Syria, the group's de facto capital, the source said.

The source inside Mosul said a tunnel network is growing, including one big enough for motorbikes, from the outskirts of the city to the nearby village of Hamdania.

A man imprisoned by Daesh in Mosul for two months said he was forced to help dig more than 12 tunnels on the eastern side of the city.

Among the groups joining to fight Daesh in Mosul are the Hashd Al-Shaabi, or Popular Mobilization Unit.

Some 9,000 Sunni fighters are part of the PMU, said Ahmed al-Assadi, a PMU spokesman. He said the PMU forces also include Christians, Yazidis and Turkmen.