A ceasefire in south-west Syria due to take effect on Sunday is a "hopeful step," according to US National Security Advisor HR McMaster.
The US-Russian-Jordanian brokered deal is to be enforced by midday on Sunday, in the provinces of Daraa, Sweida and Quneitra in the south west, along the Jordanian border.
Similar agreements have been brokered in Syria in the past with the aim of getting the country's peace process back on track following a prolonged civil war that began in 2011.
All have failed to halt the fighting for very long.
But in his statement issued late on Saturday, McMaster said the US was "encouraged by the progress made to reach this agreement".
"The United States remains committed to defeating ISIS, helping to end the conflict in Syria, reducing suffering, and enabling people to return to their homes," he added. "This agreement is an important step toward these common goals."
The deal was the result of a two-hour meeting between Russian President Vladimir Putin and his US counterpart, Donald Trump, on the sidelines of the Group of 20 summit in Hamburg on Friday.
Syrian rivals are to come together for a seventh time in Geneva on Monday, a few days after a meeting in Kazakhstan.
