Russia and the United States struggled to find agreement on a nationwide cease-fire in Syria, and Russian diplomats suggested Washington officials were to blame for the protracted talks.
At meetings in Geneva on September 9, Foreign Minister Sergei Lavrov said the talks might be called off for the day, and resumed next week.
A State Department official, meanwhile, said discussions were continuing into the evening over unspecified technical issues.
With the Syrian war now in its sixth year, and hundreds of thousands killed, Washington and Moscow have repeatedly been at loggerheads over an agreement to halt fighting between Syria's Russian-backed government and U.S.-supported rebels. Humanitarian aid to beseiged areas is also central.
Similar efforts at a cease-fire deal have failed in recent months.
Moscow has supported the regime of President Bashar al-Assad, but Washington has made no secret of its desire to see Assad leave power.
With reporting by AP, Reuters