The US will not pull its troops out of Syria until Washington's goals are accomplished, Nikki Haley, the US ambassador to the UN, said.
According to Haley, the three aims for the US are ensuring chemical weapons are not used in any way that poses a risk to US interests; Islamic State of Iraq and the Levant (ISIL, also known as ISIS) is defeated; and there is a good vantage point to watch what Iran is doing.
"It is our goal to see American troops come home, but we are not going to leave until we know we have accomplished those things," Haley said on Fox News on Sunday.
In a separate interview, Haley said that the US was preparing new sanctions on Russia over its continued support of Syrian President Bashar-al Assad.
The sanctions would be announced by US Treasury Secretary Steven Mnuchin on Monday, Haley said on CBS.
"They will go directly to any sort of companies that were dealing with equipment related to Assad and chemical weapons use," she said.
Haley also ruled out any one-on-one talks between President Assad and the US over the Syrian crisis.
She said Syria had so far refused to take part in multilateral negotiations as part of a political process facilitated by the UN, adding that Syria was not "worthy" of direct talks with Washington.
Also on Sunday, French President Emmanuel Macron said he had convinced Trump to maintain troops in Syria.
"We convinced him it was necessary to remain there. We have complete international legitimacy to act in this framework," Macron said in an interview broadcast by BFM TV, RMC radio and Mediapart online news.
"We have three members of the [United Nations] Security Council who have intervened."