UNITED NATIONS: The United States on Tuesday voiced the hope that momentum in talks aimed at hammering out a peace plan to end Syria's nearly five-year civil war could continue, and said the next meeting of major world powers could take place this month in New York.

"There is significant enthusiasm to keep the momentum going, particularly with regard to thinking through whether local ceasefires might be possible on an expedited basis," U.S. Ambassador to the United Nations Samantha Power told reporters.

"Our ambition is certainly to do another ministerial meeting in December and we're ... open to a number of different venues, one of which is New York," she said.

The first two rounds of talks on Syria among major Western and Middle Eastern powers were held in Vienna.

Syrian government officials said on Tuesday they had agreed on a deal for opposition fighters to withdraw from the last insurgent-held area of the city of Homs as part of a local ceasefire agreement.

Power said a separate upcoming meeting in Saudi Arabia of Syrian opposition figures, also expected this month, was "critically important." Riyadh issued invitations to 65 Syrian opposition figures to try to unify their positions ahead of the next round of Syria peace talks.

The Riyadh meeting is an attempt to bring together rival groups whose disunity has been an obstacle to ending a war that has killed more than 250,000 people, displaced millions and allowed the Islamic State group to seize control of parts of Syria and Iraq.

Power said Jordan was working to determine which groups opposed to Syrian President Bashar al-Assad would be invited to the peace talks.

"Jordan was given the task of working through that," she said. "We're waiting to hear from Jordan."

The biggest hurdles in the talks at the moment, diplomats have said, are the future of Assad, who Western and Gulf Arab powers want ousted, and identifying moderate opposition groups.

While all participants in the Syria talks oppose Islamic State, Western diplomats have said that Iran and Russia, which support Assad and have intervened militarily on his side, have very different views from Western and Gulf countries about which rebels are moderate.

Western nations and some rebel groups have accused Russia of targeting moderate opposition fighters with air strikes in Syria and not Islamic State.