ERBIL, Iraq — Mosul’s residents are hoarding food and furtively scrawling resistance slogans on walls, while the city’s Islamic State rulers have feverishly expanded their underground tunnel network and tried to dodge American drones.
After months of maneuvering, the Iraqi government’s battle to reclaim Mosul, the sprawling city whose million-plus population lent the most credence to the Islamic State’s claim to rule a fledgling nation, has finally begun. In the early hours Monday, an announcement by Prime Minister Haider al-Abadi of the campaign’s opening was accompanied by artillery barrages and a rush of armored vehicles toward the front a few miles from the city’s limits.
Those forces will fight to enter a city where for weeks the harsh authoritarian rule of the Islamic State, also known as ISIS, ISIL or Daesh, has sought to crack down on a population eager to either escape or rebel, according to interviews with roughly three dozen people from Mosul. Among them were refugees who managed to sneak out in recent weeks and residents reached by contraband cellphones in the city.
Just getting out of Mosul had become difficult and dangerous: Those who were caught faced million-dinar fines, unless they were former members of the Iraqi Army or police, in which case the punishment was beheading.
While the civilians described stockpiling food in basement hiding places, the jihadists were said to be frantically making military preparations within Mosul, temporarily fleeing the streets — most likely to an extensive tunnel network below — at the first signs of an airstrike, according to the new accounts.
Some of Mosul’s remaining one million or more residents had grown bolder in showing resistance to the Islamic State force ruling the city — numbering 3,000 to 4,500 fighters, the United States military estimated. Graffiti and other displays of dissidence against the Islamic State were more common in recent weeks, as were executions when the vandals were caught.
Early this month, 58 people were executed for their role in a plot to overturn the Islamic State that was led by an aide of the group’s leader, Abu Bakr al-Baghdadi, Reuters reported.
When fewer than 1,000 Islamic State fighters forced about 60,000 Iraqi Army and police defenders to abandon Mosul in June 2014, many among its Sunni population cheered their arrival. They saw the militants as fellow Sunnis who would end corruption and abuse at the hands of the Shiite-dominated Iraqi government and security services.
But much of that local good will dissipated after more than two years of harsh rule by the militants, a mix of Iraqis and Syrians with a grab bag of foreign fighters.
Mosul residents chafed under social codes banning smoking and calling for splashing acid on body tattoos, summary executions of perceived opponents, whippings of those who missed prayers or trimmed their beards, and destroying “un-Islamic” historical monuments.
“Anyone who has accepted Daesh before? They’ve changed their minds now,” said Azhar Mahmoud, a former Education Ministry official who recently fled his home village near Mosul, and who initially accepted rule by the Islamic State.
In addition, there were recent reports of at least some underground resistance within the city, if mostly symbolic. Photos and oral accounts abounded of the Arabic letter M scrawled on walls — standing for moqawama, or resistance. The Islamic State beheaded two men in front of one such slogan, and posted a video of the killings.
Another execution video identified the victims, punished for internet use, as members of the resistance group Suraya Rimah, according to the group’s leader, Omar Fadil al-Alaf, who is based in the Kurdish regional capital of Erbil, about 50 miles east of Mosul.
“People are just waiting for liberation so they can fulfill their promises to take revenge on Daesh and kill them,” Mr. Alaf said.
Compounding the militants’ problems with the population was a growing economic crisis, according to American officials. In recent months, the Islamic State lost control of oil fields near Raqqa in Syria and Qaiyara in Iraq, and trade with ISIS-held parts of Syria was choked off because of the group’s military reversals.
Electricity, once plentiful before Kurdish forces took back the Mosul Dam from militant control, has been typically available for only a couple of hours a day, residents say. Some areas lack running water, with residents forced to use personal generators to pump water from wells.
Schools had not opened at all this year, absent funding and teachers willing to work for nothing.
The local economic crisis hit the militants as well, with reports that they cut the pay for their fighters to less than $100 a month, from $400 in 2014, said Abu Bakr Kanan, a former leader of the Sunni religious affairs office in Mosul, who said he was in regular touch with residents there.
Many of the residents contacted described the militants as conducting a high-profile recruiting drive among 14- to 40-year-old males, depicting enlistment as a religious duty, but with apparently decreasing success.
A car mechanic who left the city just over two weeks ago, and asked not to be identified because he still had relatives there, said that on his final Friday in Mosul he attended prayers at which a prominent Islamic State imam harangued the worshipers about volunteering, but seemingly won no one over.
The militants’ security preparations have been directed not only at the city’s borders — particularly toward the south and east where Iraqi forces, allied militias and Kurdish pesh merga fighters are arrayed — but also internally. Traffic on secondary roads in the city was banned, and house-to-house searches — for weapons and any signs of organized resistance — were carried out in many neighborhoods.
Last month, a YouTube video surfaced of Suraya Rimah fighters appealing to residents of Mosul to kill their Islamic State rulers when the offensive began.
Resistance groups in the city — at least five claimed to have a presence — say they concentrated on assassinating individuals, said Abdullah Abu Ahmed, who described himself as a leader of an anti-ISIS brigade in Mosul called The Resistance. He was reached by telephone through intermediaries.
“All Mosul people, whenever they have the chance to fight and kill ISIS terrorists, they do so,” he said. He cited a recent attack on a jewelry market in which two members of the Islamic State were killed.
Over the past few weeks, coalition airstrikes began more intensively targeting the suspected homes of senior Islamic State figures in Mosul. Residents said those senior militants, many of whom had relatively high public profiles in the city, became conspicuous by their absence on the streets.
There have also been a notable number of desertions from the Islamic State. Kurdish officials said they had found 300 suspected deserters, or potential infiltrators, in recent months. Most were caught among the refugees escaping from ISIS-held territory who arrived at the Kurdish-run Dibaga Camp, the main site for refugees, south of Erbil, said Ardalan Mohiadin, who is in charge of the camp’s reception center.
Dibaga Camp now has 43,000 refugees from Mosul and other Islamic State strongholds, with about 11,000 arriving in September alone, Mr. Mohiadin said.
Despite months of preparation for a much larger wave of refugees from the city, aid officials warned that it was unlikely to be nearly enough once the fighting intensified.
“The United Nations is deeply concerned that in a worst-case scenario, the operation in Mosul could be the most complex and largest in the world in 2016, and we fear as many as one million civilians may be forced to flee their homes,” said Lise Grande, the United Nations’ humanitarian coordinator for Iraq.
Airstrikes on the militants in Mosul led many of them to move in among civilian residents, the locals said.
A woman who arrived at Dibaga Camp recently said her family had been forced to take in a Chechen ISIS fighter, and shortly afterward an airstrike hit the home, killing the militant but also two members of the family. The woman’s 9-year-old daughter was trapped under a collapsed wall.
The girl survived and is with her mother in the camp now.
Nearly all of the Mosul residents contacted spoke on condition of anonymity for fear of Islamic State retaliation. Even most refugees did not want to be identified because they still had relatives in Mosul.
“We are suffering from so many problems, we feel like the living dead,” said a woman who identified herself only by the initials S. A.
In addition to American air support, President Obama this month approved 615 more American troops to aid the Mosul offensive by providing intelligence and logistical assistance. That brings the American forces in Iraq to more than 5,000.
Some in Mosul described how militants had begun going house to house to collect used tires that could be set on fire to generate smoke screens.
“We expect everything,” said Sabah al-Numan, the spokesman for the Iraqi Counterterrorism Force. “We know this is the last station for ISIS — there is nowhere else for them to go. We have to prepare for a very tough fight.”
Reporting was contributed by Jamal al-Badrani and Kamil Kakol from Erbil, Falih Hassan and Omar Al-Jawoshy from Baghdad, and Michael R. Gordon from northern Iraq.