US-backed force tightens noose on IS-held Raqqa hospital

US-backed fighters were tightening the noose around Islamic State group militants holed up in Raqqa's national hospital on Sunday, one of the last IS-held positions in the Syrian city.

The Syrian Democratic Forces manned positions on the fourth floor of a heavily damaged building overlooking the hospital less than 150 metres (yards) away.

"We're at the end of Raqqa. There are two positions left: the stadium and the few surrounding buildings, and the national hospital," said Amjad Siryani, a local commander with the SDF's Syriac Military Council.

Siryani, 28, said his position was around 120 metres from the hospital where IS snipers, too, were watching.

"One of our comrades was hit by a sniper in his leg. We were able to identify where the shot came from and shoot him down," the gangly fighter told AFP.

The SDF has ousted IS from around 90 percent of the battered northern city but the militants still hold a pocket of central Raqqa.

SDF fighters and IS exchanged rocket and mortar fire throughout the day on Sunday, and several airstrikes by US-led coalition warplanes could be heard across the city.

The US-backed Kurdish and Arab fighters are positioned around the hospital in several multiple-storey buildings, many of them hollowed-out concrete carcasses of apartment complexes.

Children used as shields

The command posts were in constant coordination through a network of walkie-talkies: orders, calls for help, and messages of support crackled through in Arabic, Kurdish, Turkish, and even Syriac.

The SDF's goal, its fighters said, was to isolate the IS-held hospital from the stadium to the northwest, but they have yet to break into either position.

"The reason we haven't stormed the hospital yet is because there are civilians there," said Siryani, who said he had seen militants use children as human shields near the complex.

In a nearby position, SDF fighter Mohammad Selmo said he was often tasked with monitoring the hospital overnight and had heard crying children from inside.

"We are observing and waiting for the order to storm the hospital. If we see anyone coming out of it, they die," the young fighter told AFP.

"Once we take the hospital, it's over. It's important because there are a lot of IS fighters there, but the Americans cannot just bomb it."

Selmo and other SDF fighters said they had understood coalition warplanes would not target the medical facility because of the presence of civilians.

The US-led coalition has said that it and the SDF are aware of reports that civilians inside are being used as human shields.

Raqqa was the first city to fall out of Syrian government hands after the uprising against President Bashar al-Assad broke out in 2011.

It first fell into rebels but IS militants seized it in early 2014, transforming it into the de facto Syrian capital of their so-called caliphate.

Agencies contributed to this report.