One of the members of the Syrian Democratic Forces tasked with monitoring the Raqa hospital says Islamic State group jihadists are using children as human shields (AFP Photo/BULENT KILIC)

A Syrian Democratic Forces (SDF) member runs to take cover from sniper shots in the Syrian city of Raqa in October, where Syrian fighters with US military support cleared the last remaining Islamic State group jihadists holed up in their crumbling stronghold (AFP Photo/BULENT KILIC)

Raqa (Syria) (AFP) - US-backed fighters were tightening the noose on Sunday around Islamic State group jihadists holed up in Raqa's national hospital, one of the last IS-held positions in the Syrian city.

The Syrian Democratic Forces have ousted IS from around 90 percent of the battered northern city but the jihadists still hold a pocket of central Raqa.

Less than 150 metres (yards) west of the hospital on Sunday, SDF fighters manned positions on the fourth floor of a heavily damaged building overlooking the hospital and the no-man's land below.

Periodically, they fired heavy machineguns at the massive complex then monitored carefully to identify the source of the returning fire.

"We're at the end of Raqa. 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.

That successful shot elicited animated whoops from his fellow militiamen, who had hung IS's black notorious flag in their position as a trophy.

SDF fighters and IS exchanged rocket and mortar fire throughout the day on Sunday, and several air strikes 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 jihadists 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.

Raqa 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 jihadists seized it in early 2014, transforming it into the de facto Syrian capital of their so-called caliphate.