Only one health facility remains operational in the Islamic State-held part of Raqqa, serving thousands of civilians trapped in the Syrian city with virtually no emergency services or rescue personnel, as the intense U.S.-backed campaign to liberate the city continues, Physicians for Human Rights said Friday.

The New York-based group described "nightmarish" conditions in the ever-shrinking area controlled by Islamic State militants amid an incessant bombing campaign. Wounded civilians are left under the rubble because neighbors fear being trapped by further airstrikes. The lone operating hospital is using saltwater to sanitize wounds, and treatment of traumatic injuries is limited to stopping the bleeding, the group said based on interviews it carried out with survivors, physicians and aid workers from the city.

The U.S.-led campaign, which began in earnest in June, left only the national hospital functioning and even that at reduced capacity, as others were either bombed or closed, the group said.

One doctor who escaped in mid-August told PHR that he operated out of his home because civilians feared going to the hospital in case it was shelled, or to avoid extortion by Islamic State fighters. Militants from the extremist group administer the hospital, which has been divided into two sections, one for civilians and another for the group's members. Amid the campaign, the last of the hospital's remaining services were forced underground, providing very basic medical care, PHR said.

In recent weeks, medical supplies have dwindled and pharmacies closed. The doctor finally left Raqqa after two of his colleagues were killed in airstrikes that hit their homes. As he fled, his daughter was killed in a land mine explosion.

"Raqqa is a deathtrap where civilians who have already suffered for years under [Islamic State] rule now also suffer the deadly consequences of the fight against [the Islamic State]," said Racha Mouawieh, Syria researcher for PHR.

The United Nations has estimated that as many as 25,000 civilians remain trapped in the city, unable to leave either because the militant group holds them to use as human shields or because of land mines along the roads and the heavy bombing.

For those who escape the city, the closest health facility is 50 miles away, in Tal Abyad, or 90 miles away in Kobane for a specialized trauma unit. A new private hospital opened in Tabqa, about 25 miles from Raqqa, last week, PHR said.

The group called on parties to the conflict to ensure civilian access to medical care and safe evacuation.

The U.S.-led coalition has said that it does everything "within its powers" to limit harm to civilians but that casualties are inevitable in a street-by-street battle with the militants.

Since the campaign began in June, U.S.-backed Syrian fighters have seized more than 60 percent of the city, tightening the noose on hundreds of Islamic State militants who are fighting to the death for the city — and trapping thousands of civilians with them. The U.N. and rights groups have expressed concern for civilian safety, with one official urging a "humanitarian pause."