The US Marines will provide logistical support to local forces who are preparing to move against Daesh in Raqqa.
The US has deployed Marines armed with heavy artillery to Syria ahead of a planned offensive against Daesh in the northern city of Raqqa.
The move comes just days after the Pentagon announced the deployment of dozens of US ground troops on the outskirts of the YPG-controlled town of Manbij.
The Pentagon on Monday said the deployment to Manbij would serve as a "visible sign of deterrence and reassurance," in what appears to be an attempt to ensure that Turkish-backed Free Syrian Army (FSA) opposition forces do not clash with the US-backed YPG.
While the US views the YPG as an ally in the fight against Daesh, Turkey considers the group to be an affiliate of the PKK. Turkey and the US, both NATO members, list the PKK as a terrorist organisation.
A senior US official said the deployed Marines are "pre-positioning howitzers to be ready to assist local Syrian forces," without referring to a specific group.
The official also said that hundreds of Marines would also be deployed to Kuwait, where they will remain on standby to be called into action against Daesh if necessary.
Expanded US role
US military commanders in Syria were restricted by what critics considered micro-management under the previous administration of Barack Obama. They want greater freedom and flexibility to make daily combat decisions without going to the White House for approval every time.
Existing restrictions limit the US to stationing no more than 503 forces permanently in Syria.
But in a letter to the White House last month, Pentagon leaders appealed for an increase in order to better advise allied fighters ahead of the battle for Raqqa.
They also requested increased artillery support, more Apache helicopters and a more robust training campaign.
Raqqa is Daesh's de facto capital in Syria. The terrorist group occupied the city in 2013 in a security vacuum resulting from the Syrian civil war.
The group expanded in 2014, capturing the Iraqi city of Mosul and declaring a "caliphate" in the region.
A multi-front battle ensued, and Daesh has lost ground on both sides of the border, even as the civil war rages on in Syria.
The fight against Daesh in and around Raqqa is being slowed by the presence of civilians, who risk being caught in the crossfire.
Suspected US-led coalition air strikes killed 14 civilians in northern Syria on Thursday, including six children, Rami Abdel Rahman of the Syrian Observatory for Human Rights said.
"The raids hit the village of Al-Matab after midnight and were likely carried out by the coalition," he said.
The village is about 55 kilometres southeast of Raqqa.
US officials believe there are still around 300,000 civilians in Raqqa at risk of being used as human shields by some 4,000 Daesh fighters.