"We're going to continue to make the case to the opposition that they should participate in the talks, that is the path that will resolve the core of this issue," Earnest said.
Washington will encourage all parties to live up to ceasefire in Syria, Earnest went on, adding that Russia should use "influence they have with the Assad regime to compel them to live up to the commitments that they made under the cessation of hostilities and get back to the negotiating table in a constructive way."
Earnest’s remarks come as Syria’s opposition High Negotiations Committee (HNC) put its participation in the intra-Syria talks on hold on Monday.
The new round of intra-Syrian talks began in Geneva on April 13, and was supposed to focus on Syria's political transition and governance.
