After storming the Iraqi city of Mosul in June, the brutal Islamic State quickly solidified its control. Gunmen enforced its laws, and supportive imams preached at the mosques.

But the militants were missing something -- doctors. So last month, the Islamic State issued an ultimatum to physicians who had fled: Return to work, or we'll seize your property and you can never come back.

The Islamic State's efforts to run Mosul's health-care system provide a glimpse into its efforts to build a caliphate, or Islamic state, in Iraq and Syria. Despite their victories on the battlefield, the militants have struggled as everyday administrators in Mosul, with the city's hospitals grappling with daily power outages and shortages of medicine. The Sunni fighters have also imposed measures that have alienated staff and compromised the lives of patients, doctors say.

The Islamic State's rigidity and inexperience may ultimately cost it's support in areas where some Sunni residents initially welcomed the group as an alternative to the Shiite-led central government. Already, the Islamic State has been forced to give ground on some of its stringent policies, such as barring male and female doctors from working together.

But the group continues to impose a harsh version of Islamic rule, according to medical personnel at four of the city's seven hospitals, who spoke via telephone on the condition of anonymity because of security concerns. Female staff members, including doctors, are not allowed to work night shifts at the hospitals, they said. Female doctors must wear full-face veils.

Little dissent is tolerated. One doctor in Mosul said that earlier this month, he witnessed a patient arguing with a physician affiliated with the Islamic State. The next day, militants brought the patient to the hospital lobby, where they whipped him and forced him to apologize to the physician.

"Of course, those of us who didn't join them, we are all living in fear," the doctor said.

The Islamic State emerged as a major player in the Syrian civil war in 2012 and 2013, and first tried governing in smaller cities in rural Syria. In its de facto capital in Raqqa -- which has about 570,000 residents -- the group has established Islamic law courts and revived clinics damaged by the war between the rebels and the Syrian government. It has even managed to run nearby oil refineries.

An August report by REACH, a U.N.-linked disaster-mapping service, said basic services in the Syrian city were reported to have improved somewhat after the Islamic State took over in January, after months of battles that had crippled much of the infrastructure.

But Mosul, in Iraq's north, is about twice as populous. And unlike Raqqa, which is part of an extensive region controlled by the Islamic State, Mosul has been largely isolated since it fell to the militants in June. The central government in Baghdad shut off its power supply, and Iraqi security forces, Shiite militias and Kurdish peshmerga forces control roads into Mosul.

"Mosul is a big city. It's very difficult to govern," said Ahmed Ali, Iraq senior research analyst at the Institute for the Study of War in Washington. Islamic State fighters, he said, "want to project an image of efficiency. But they are also very much improvising on the fly."

One of the Islamic State's first edicts after taking over Mosul was to impose a dress code for female staff members at the city's hospitals, requiring them to wear head scarves, full-face veils and gloves.

The decree shocked a city in which most women dress conservatively but had never been forced to cover their faces while working.

Then the fighters moved to abolish family-planning programs and halted the distribution of contraceptives, which had been available to married couples.

One night over the summer, Islamic State officials prevented a male anesthesiologist from treating a woman in labor, a doctor said. The extremists deemed it improper for the anesthesiologist to see another man's wife giving birth. With no women allowed to work the late shift, the pregnant woman went without medication. (Because female obstetricians command slightly more respect from the militants, one could be called in at night if needed.)

Although the militants try to retain local bureaucrats to keep institutions functioning, they promote loyalists and commanders to top government positions, including at the hospitals.

"They are fighters, and this is civilian work," said a female doctor. "The people are not their priority."

In September and October, at least five doctors -- men and women -- were killed in Mosul, rights activists in northern Iraq said. The activists said it was unclear whether the doctors were executed because of their work. Also in October, the activists said, militants arrested a pharmacist for selling medicine to a woman who was not considered properly veiled. The pharmacist has not been heard from since.

But amid the terror, the jihadists have had to relax some of their harsh measures, and they have worked to keep the health sector afloat.

The dress code for women prompted a strike by female personnel at local hospitals. A compromise was eventually reached. While female staff must still be covered, the doctors said, they are now largely allowed to mingle with male co-workers and patients so as not to hinder care.

The militants have also allowed some female patients to see male specialists for ailments that are unrelated to pregnancy or sexual organs -- such as a broken arm, for example, medical professionals said.

Citing concerns about its budget, the Islamic State in Mosul has allowed hospital staff to continue to receive salaries from the central Iraqi government in Baghdad. The local Islamic State administrators said they could pay doctors a monthly salary of only $200 per month, while the physicians receive roughly $1,000 from the government, the doctors said.

So now the fighters permit a single hospital employee to travel each month to nearby Kirkuk -- which is controlled by northern Iraq's Kurdistan Regional Government -- to get the cash from government-approved banks, according to the medical personnel.

The jihadists have also smuggled in basic medications to be distributed at public hospitals and clinics, where drugs had routinely been provided free by Iraq's government.

"We try to deliver medicine and supplies [to Mosul], but it's very difficult," said Iraq's Health Ministry spokesman, Abdel Ghani Saadoun. "We don't want it to end up in the hands of Daesh," he said, using an Arabic acronym for the Islamic State.

The smuggling routes that crisscross Mosul and its environs are some of the city's few lifelines for food, fuel and medicine. Mosul's residents and pharmacies use the corridors to bring in their own medicine, often at double or triple the normal price.

The militants in Mosul tolerate the practice. That appears to be in stark contrast to their behavior in Syria, where Islamic State militants have obstructed the importation of medicine by medical personnel to the eastern Hasakah province, the United Nations recently reported.

Just over a month ago, however, the Islamic State limited the amount of profit that Mosul's pharmacists can make selling smuggled medication, doctors said. The order was aimed at helping poverty-stricken residents.

More-sophisticated prescription drugs and long-term treatments have become more difficult, if not impossible, to access. A surgeon said the orthopedic clinic at one hospital, which had seen 60 paraplegic patients since June, had run out of wheelchairs.

One of the Islamic State's most harmful actions, doctors said, was to pilfer Mosul's blood bank to treat its wounded fighters. In August, the United States began its bombing campaign against militants who had seized the Mosul Dam. Hundreds of Islamic State fighters were injured, and the extremist group ordered doctors to use the blood for transfusions. Now civilian patients must bring their own blood donors to the lab.

But with the constantly flickering electricity, much of it cannot be stored safely.

"There is no life here, we live in the dark," the female doctor said. "In Mosul, we are like the living dead."