U.S. Ambassador Nikki Haley says Syrian President Bashar Assad is "a war criminal" who has been an obstacle to peace for years -- but she says the United States isn't ruling out co-operating with him to defeat the Islamic State extremist group.

Haley told a news conference Friday that what Assad has done to the Syrian people "disgusting."

She echoed the Trump administration's declaration on Friday making clear that the U.S. focus is on defeating IS. She said last week it wasn't pursuing a strategy to push Assad out of power.

Haley said Friday the U.S. focus is on negotiations in Geneva aimed at ending the more than six-year Syrian conflict, though that could change.

"Right now Assad is not our number one person to talk to," she said.