The US is sending 200 more military personnel to help fight the Islamic State group in its Syrian stronghold of Raqqa, the US defence secretary says.
Speaking at talks on Middle East security, Ash Carter said the troops would include special forces trainers, advisers and bomb disposal teams.
They will join 300 US special forces who are already in Syria.
Last month a US-backed coalition of Kurdish and Arab fighters said it had begun an operation to capture Raqqa.
The Syria Democratic Forces (SDF) had been gaining ground in areas north of the so-called Islamic State's "capital" in Syria.
Speaking on Saturday at a meeting in Bahrain, Mr Carter said the 200 additional troops would "continue organising, training, equipping, and otherwise enabling capable, motivated, local forces" to take the fight to IS.
Interactive See how the area IS controls has changed since 2015
A US-led coalition has been fighting IS - mainly through air strikes - in Syria and in neighbouring Iraq.
But the main conflict in Syria pits the government of President Bashar al-Assad - assisted by Russian air power - against rebels backed by Turkey, Gulf states and the US.
One key battleground is Aleppo, once Syria's largest city, where pro-government forces continue their advance in eastern, rebel-held areas.
In a BBC interview broadcast on Saturday, the UN special envoy for Syria warned that a government victory in Aleppo would not end the war.
"A serious discussion about the future political set-up of Syria" is the only way to achieve peace, Staffan de Mistura told BBC Radio 4's Today.
The only way to win peace and stability in Syria, he continued, was a power-sharing agreement.
Syria's army seized 85% of the rebel-held part of the city in recent weeks.
The intensification in fighting has forced tens of thousands to seek refuge in government-controlled territory.
Russian officials say up to 10,500 left during a temporary humanitarian pause on Thursday alone.
Mr Carter added that Russia, Syria's main ally, had "only inflamed the civil war and prolonged suffering".
'Worst conflict since WWII'
Meanwhile, foreign ministers from the US and Europe, as well as officials from Arab countries are discussing the Syrian conflict in Paris.
Saturday's talks were expected to focus on ways to protect civilians, as well as the future of the rebels in eastern Aleppo.
US Secretary of State John Kerry, who is attending the talks, sought to lower expectations saying: "I know people are tired of these meetings, I'm tired of these meetings.
"But what am I supposed to do? Go home and have a nice weekend in Massachusetts, while people are dying? Sit there in Washington and do nothing?"
He described the conflict in Aleppo as the worst "since World War Two".
The UN estimates that up to 100,000 people are squeezed into an "ever-shrinking" rebel pocket in eastern Aleppo with little or no access to food or water.
Aleppo was once Syria's commercial and industrial hub before the uprising against President Assad began in 2011.
It has been divided in roughly two since mid-2012. But in the past year, Syrian troops broke the deadlock with the help of Iranian-backed militias and Russian air strikes.