BEIRUT (Reuters) - The U.S.-led coalition fighting Islamic State has boosted support for its Syrian allies, supplying armored vehicles for the first time as they prepare for a new phase in their campaign to capture Raqqa, a spokesman for the militia said on Tuesday.

A Syrian army soldier stands guard as visitors walk inside Aleppo's Umayyad mosque, Syria January 31, 2017. REUTERS/Omar Sanadiki

The U.S.-backed Syrian Democratic Forces (SDF) alliance, which is dominated by the Kurdish YPG militia, is waging a campaign to capture Islamic State’s base of operations in Raqqa.

A Kurdish military source, speaking on condition of anonymity, told Reuters the next phase of the Raqqa campaign would aim to seal off all remaining roads to the city, including the route to Deir al-Zor province, another IS stronghold.

The SDF is likely to figure prominently in U.S. President Donald Trump’s strategy for fighting Islamic State in Syria, where the jihadist group still holds large areas of territory stretching to the Iraqi border.

SDF spokesman Talal Silo said the delivery of the armored vehicles marked a significant improvement in U.S. support and attributed the change to the new administration. Trump says eradicating Islamic State will be one of his biggest priorities.

“Previously we didn’t get support in this form, we would get light weapons and ammunition,” Silo told Reuters. “There are signs of full support from the new American leadership -- more than before -- for our forces.”

A Pentagon spokesman said the vehicles had been supplied to the Syrian Arab Coalition - part of the SDF - and would help it contend with the threat posed by improvised explosive devices used by Islamic State as they advance towards Raqqa. He said there had been no change of policy.

“The Department of Defense only provides training and materiel support to the Syrian Arab Coalition,” Major Adrian J.T. Rankine-Galloway said in a statement.

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The U.S. strategy towards fighting Islamic State in Syria has generated tension with NATO ally Turkey, which views the YPG as an extension of the Kurdistan Workers Party (PKK), a group that has waged a three-decade insurgency in southeast Turkey.

The YPG forms the military backbone of autonomous regions set up by Kurdish groups and their allies in northern Syria since the onset of the war in 2011.

Trump, who pledged in his inaugural address to wipe Islamic State and like-minded groups “from the face of the Earth”, signed an executive order on Saturday asking the Pentagon, the joint chiefs of staff and other agencies to submit a preliminary plan on how to proceed within 30 days.

Islamic State is being fought in Syria by three sets of enemies: the Syrian Democratic Forces in northern Syria, the Syrian government and its Russian and Iranian-backed militia allies in central and eastern Syria, and the Turkish army and its Syrian rebel allies in a strip of land near the border.

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The SDF launched a campaign with the ultimate aim of capturing Raqqa in November. The first two phases focused on capturing areas to the north and west of Raqqa, part of a strategy to encircle the city.

The Kurdish military source said the third phase would focus on capturing remaining areas, including the road between Raqqa city and Deir al-Zor. Cutting off Raqqa city from IS strongholds in Deir al-Zor would be a major blow against the group.

“The coming phase of the campaign aims to isolate Raqqa completely,” said the Kurdish military source, who declined to be named. “Accomplishing this requires reaching the Raqqa-Deir al-Zor road,” the source said.

“It will be difficult because Raqqa is not a place Daesh will easily give up,” said the source, using the Arabic acronym for Islamic State.

Silo of the SDF said preparations were underway for “new action” starting in “a few days”, but gave no further details.

SDF forces had advanced to within 1 km (half a mile) of the Islamic State-held Euphrates Dam to the west of Raqqa, but have yet to capture it, Silo said, adding that air power could not be used there in case the dam was damaged.

The Syrian Observatory for Human Rights, which reports on the war, said the SDF’s progress near the dam had come to a halt due to IS resistance.

Islamic State has been fighting hard in recent weeks to try to capture the last remaining pockets of Syrian government-held territory in Deir al-Zor city, prompting Russia to dispatch long-range bombers to repel its assault.