Ammar Al Shamary and Gilgamesh Nabeel

Special for USA TODAY

BAGHDAD — For months, the Iraqi government has been preparing to launch an offensive to recapture the country's second largest city, Mosul, from the Islamic State. Now, there are clear signs that the militants believe it is imminent.

The extremist group's fighters have sent their wives and children to Syria and Turkey, pulled their black flags from buildings to hide potential airstrike targets for a U.S.-led coalition, planted roadside bombs and set fires to oil wells to stymie Iraqi troops.

The Islamic State “has announced its highest alert,” said Arm Khaled al Obaidi, a Mosul resident and former policemen. “They canceled all leave and demanded fighters on leave return to duty."

This month, Iraqi forces recaptured from the militants an airstrip about 40 miles south of Mosul that will serve as an important staging area for Iraqi troops. At the same time, the U.S. military said it is sending an additional 560 troops to Iraq for duties that include guarding the air base in anticipation of the long-promised siege.

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Mosul is the Islamic State’s last power center in the country. Iraqi forces already recaptured Fallujah — about 40 miles west of Baghdad — and other cities that the militant group had controlled since invading the country two years ago.

Iraqi Prime Minister Haider al-Abadi pledged to retake Mosul before the end of the year, but it’s not clear when an offensive could begin in earnest.

Mosul resident Faisal Essawi said now is the time to confront the Islamic State because some fighters are deserting the group in anticipation of an epic battle.

“The government must take the opportunity of the chaos (the Islamic State) is suffering after losing the airbase,” Essawi said. "Some of their leaders have gone missing. The organization is struggling to fill the gap.”

Iraqi officer Abu Mohamad said the Islamic State is getting desperate. It "set up fixed and mobile checkpoints to hunt down their own fighters who fled the front, the battle near the air base," he said. "They have also started looking for former policemen and soldiers to arrest them, as they consider them a potential threat."

Some Iraqis who already fled Mosul said other residents are now trying to escape because they fear Iraqi Shiite militias fighting alongside government troops. Mosul's largely Sunni Muslim residents have heard news reports about militiamen who abducted, tortured and executed Fallujah residents suspected of cooperating with the Islamic State. Fallujah also is predominantly Sunni, the same sect as the militants.

“Some are afraid of the militias, not the army, as they might seek revenge from the city’s residents,” said Abu Ahmed, 30, a medical technician in Germany. He fled Mosul last year with the help of smugglers but still keeps in close contact with his family in the city.

“My brother, a teacher in Mosul, said that the Islamic State exploits videos of violations in Fallujah to frighten people," he said. "They display them in media centers in streets and distribute them as CDs.”

The worry about the Shiite militias illustrates how Mosul's Sunni residents are torn between allegiances. Many opposed the corrupt, mostly Shiite Iraqi army personnel that had been in Mosul, and they embraced the militant group when it ousted the government forces. But the Islamic State’s harsh interpretation of Islam, oppression and mismanagement of the city soured them on their new rulers.

"When the army was first defeated, people were very happy,” said Haider al Juburi, 38, a grocery shopkeeper in Mosul. “But now we regret that and prefer the time when the government ruled."

The Islamic State’s mishandling of the city’s economy is a major factor in their disappointment, especially the constant cuts in civil servants' salaries and new taxes.

“Taxes are imposed on trifles like the need to change the vehicle plates to carry the name of ‘Wilayah Nineveh,’” the Islamic State’s term for the province where Mosul is located, said Mohammed Al-Zakaria, 27, who fled from Mosul to Baghdad after the militants overran the city.

“They have looted teaching hospitals and houses, while other hospitals are being used for their own,” he added.

The city couldn’t continue for much longer under the Islamic State without suffering a famine, said shopkeeper al Juburi. He can charge no more than 10 cents for about a pound of tomatoes, but most people don’t even have that much to spend.

"We’ve lived through a very hard time recently,” he said. “People are starving and waiting for the arrival of the Iraqi army to end the suffering.”

Nabeel reported from Istanbul.