Turkey's invasion of northern Syria has 'revived' Islamic State, according to the Kurdish-led SDF group which has called on allied states to close off air space to Turkish war planes.

In a televised statement, senior SDF official Redur Xelil said the Syrian Democratic Forces were continuing to cooperate with the US-led coalition against Islamic State even as it must now also confront the Turkish attack on northern Syria.

'The Turkish invasion is no longer threatening the revival of Daesh [Islamic State], rather it has revived it and activated its cells in Qamishli and Hasaka and all the other areas,' Xelil said, noting car bomb attacks in each of the two cities.

'We are still cooperating until now with the international coalition to fight Daesh. We are now fighting on two fronts: one front against the Turkish invasion and a front against Daesh,' he said.

Smoke rises from targets inside Syria during the bombardment by Turkish forces at Ras al-Ain

An explosion over the Syrian town of Ras al-Ain as seen from the Turkish border town of Ceylanpinar, Sanliurfa province on Saturday

The Kurdish militia previously warned that the Turkish assault could allow the jihadist group to re-emerge as some of its followers were escaping from prisons.

In its first big attack since the assault began on Tuesday, Islamic State claimed responsibility for a deadly car bomb in Qamishli, the largest city in the Kurdish-held area.

Five Islamic State fighters fled a jail there, and foreign women from the group being held in a camp torched tents and attacked guards with sticks and stones, the SDF said.

Britain's Foreign Secretary Dominic Raab criticised Turkey's military assault against Kurdish-held parts of Syria on Saturday, saying it weakens the fight against so-called Islamic State and risks deepening the humanitarian crisis in the war-ravaged region.

Thick plumes of smoke rose around Ras al-Ain, one of two Syrian border areas targeted in the offensive as Turkey-backed forces ramped up their attack

Mr Raab said Ankara must show 'maximum restraint' as the air and ground offensive entered its fourth day, with tens of thousands fleeing their homes in north-east Syria.

Speaking at the 65th Nato Parliamentary Assembly at the QEII centre in Westminster on Saturday, Mr Raab said: 'Our position is crystal clear. This incursion is wrong. We want to see maximum restraint, and avoid taking our eye off the ball with Daesh (IS).

'My fear is that the risk is that the humanitarian situation ... could be made worse. The risk is with the counter-terrorism operation you describe, taking on the SDF and the broader objectives, is that it is weakening the overarching counter-terrorism goal of countering Daesh.

'I think the UK, like many others, is very concerned we're taking our eye off the ball. It's quite important that we have this conversation with our friends that we are mindful of their legitimate concerns.

Britain's Foreign Secretary Dominic Raab criticised Turkey's military assault against Kurdish-held parts of Syria on Saturday

Intense gunfire also resounded from within the town itself, while warplanes could be heard flying overhead, reports said

'But nonetheless I think that only serves to sharpen the focus we need to have on the actions Turkey is now taking. We need to see maximum restraint'.

Mr Raab's comments come as Turkey-backed Syrian troops claimed on Saturday they had taken over Ras al-Ain as Turkey's offensive against a Kurdish militia in the region entered its fourth day.

'The [Syrian rebel] national army took control of the town centre this morning. Inspections are being conducted in residential areas,' a senior Turkish official said.

Kurdish authorities have, however, denied this is the case. 'Ras al-Ain is still resisting and clashes are ongoing,' the Kurdish-led Syrian Democratic Forces said.

Turkish soldiers stand near military trucks in the village of Yabisa, near the Turkish-Syrian border

A Turkish police armored vehicle patrols the town of Akcakale, Sanliurfa province, southeastern Turkey, at the border with Syria

The Syrian Observatory for Human Rights also reported that the town, a major target of the Turkish offensive, had yet to be completely taken.

Turkish troops also stepped up their bombardment in northeastern Syria this weekend as the death toll rose to 74 Kurdish YPG fighters and 30 civilians.

Turkey's Defense Ministry added that 415 YPG militants had been 'neutralised' since the operation began, a term that commonly means killed.

It is believed nearly 200,000 people have been displaced as a result of the offensive, the Syrian Kurdish-led administration said.

Turkey-backed Syrian rebel fighters stand on a vehicle in the village of Yabisa, near the Turkish-Syrian border

Mourners carry the coffins of Halil Yagmur, 64 and Muslum Guzel, killed Friday during mortar shelling from Syria

Relatives mourn in front of the grave of Yagmur who was killed in a mortar attack in Suruc near northern Syria border

Turkey has said it aims to defeat the YPG, which it sees as an enemy for its links to PKK militants who have fought a decades-old insurgency in Turkey in which 40,000 people have been killed.

There has been fierce international criticism of the assault and concern about its humanitarian consequences.

On Friday evening, Turkish President Tayyip Erdoğan dismissed mounting international criticism of the operation and said Turkey 'will not stop it, no matter what anyone says'.

Turkey opened its offensive after US President Donald Trump spoke by phone on Sunday with Erdogan and withdrew US troops who had been fighting alongside Kurdish forces.

The United States has since ramped up its efforts to persuade Ankara to halt the incursion against US-backed Kurdish forces, saying Ankara was causing 'great harm' to ties and could face sanctions.

The United States has ramped up its efforts to persuade Ankara to halt the incursion against US-backed Kurdish forces

The US said Ankara was causing 'great harm' to ties and could face sanctions in the future

Earlier, the Pentagon said US troops came under artillery fire from Turkish positions on Friday but none of its soldiers were wounded, near Syria's Kobani, some 37 miles west of the main area of conflict.

Turkey's Defense Ministry said its forces did not open fire at the US base and took all precautions to prevent any harm to it while it was responding to fire from a nearby area by the Kurdish YPG militia, which Ankara regards as a terrorist group.

'US and coalition soldiers were definitely not hit. Indeed the necessary coordination is being carried out by our headquarters and the Americans,' Turkish Defence Minister Hulusi Akar said on Saturday.

The Syrian Democratic Forces, with the Kurdish YPG as its main fighting element, now holds most of the territory that once made up Islamic State's 'caliphate' in Syria, and has been keeping thousands of fighters from the jihadist group in jail and tens of thousands of their family members in camps.