Hundreds of US Marines have arrived in Syria to establish an outpost in support of the operation to retake the city of Raqqa, the de-facto Islamic State (IS, formerly ISIS/ISIL) capital in the country, the US-led coalition confirmed on Thursday.

"We are talking about an additional 400 or so forces in total, and they will be there for a temporary period," coalition spokesman US Air Force Colonel John Dorrian said, as cited by Reuters.

The deployment is an addition to the existing 500 US forces already in Syria and is aimed at accelerating the defeat of IS in its Syrian stronghold of Raqqa city, Dorrian said.

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According to the official, the additional forces would be working with local partners in Syria – the Syrian Democratic Forces (SDF) and the Syrian Arab Coalition. He stressed they would not have a frontline role.

Dorrian said the new forces comprised a Marines artillery unit and Army Rangers.

Reports of the new deployment first surfaced in US media on Wednesday.

The Washington Post, which was the first to break the news citing anonymous defense officials, stated that the marines will be working to establish an outpost from which they can fire artillery in support of the fight for Raqqa.

According to the newspaper, the new deployment is part of an amphibious task force of the 11th US Marine Expeditionary Unit, which left San Diego on Navy ships in October. It includes part of an artillery battery that can fire 155mm shells from M777 Howitzers.

The Washington Post said that the marines will be based within no more than 32km (20 miles) from the frontline outside Raqqa, as that is the maximum range of their artillery.

“The marines answer a problem that the [operation] has faced. [They now provide] all-weather fires considering how the weather is this time of year in northern Syria,” an official was cited as saying.

NBC on its part reported that the taskforce was pulled from Kuwait, also citing US defense officials, adding that the deployment is part of the new effort to “accelerate the fight” against the militants.

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The news of the US deployment comes after American soldiers were spotted traveling in an armored convoy near the Syrian city of Manbij, some 100km northwest of Raqqa, over the weekend in Strykers – heavily-armed, eight-wheel armored vehicles. The US-led coalition in Syria confirmed the presence of American forces around Manbij on Saturday, with US spokesman calling it a “deliberate action” aimed at ensuring that forces within the US-led coalition “keep the focus on defeating ISIS.”

Raqqa has an estimated 3,000-4,000 IS fighters, but the group’s leaders have been rapidly fleeing the city lately - with the advance of liberation forces, the New York Times said on Wednesday citing a US defense official. The operation to liberate the city from terrorists, codenamed Operation Euphrates Rage, was launched by the Kurdish-led Syrian Democratic Forces (SDF) on November 5, 2016.

In the most recent development, on Monday, the SDF announced that they had severed the road between Raqqa and Deir ez-Zur to the east, cutting off a supply route for the extremist group and further isolating the militants in the city, Rudaw media network reported.