The United States will send as many as 200 additional troops to help Kurdish and Arab fighters launch an assault on Islamic State's key stronghold of Raqqa.
US Defence Secretary Ash Carter said the extra troops would include special operations forces, reports the Guardian.
He said that President Barack Obama approved the troop additions last week.
Three hundred US troops are already working in the region to recruit, organise, train and advise local Syrian forces to combat the ISIS.
Addressing a security conference in Bahrain, Carter criticised US partners in the Middle East for failing to provide more military muscle in the broader campaign to defeat ISIS and counter-extremism.
Carter also said that the US had been the target of disingenuous criticism from "regional powers here in the Middle East" for not doing more to help fight extremism.
More From This Section
"I would ask you to imagine what US military and defence leaders think when they have to listen to complaints sometimes that we should do more, when it's plain to see that all too often the ones complaining aren't doing enough themselves," he said.
A senior defence official said the troop boost announced by Carter would give the US extra capability to train Arab volunteers who are joining the Raqqa push but are not well trained or equipped.