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The United States says it had not yet struck an agreement with Russia on ending the years-long conflict in Syria, blaming Moscow for reversing its position on issues it thought were settled.
The US State Department said Sunday a deal was close and could be announced by Secretary of State John Kerry and his Russian counterpart Sergei Lavrov, but hours later acknowledged they had failed to reach a deal for now.
"Russians walked back on some of the areas we thought we were agreed on, so we are going back to capitals to consult," a senior State Department official said.
Kerry and Lavrov will meet again on Monday in Hangzhou, China, where G-20 leaders are gathered, he added.
US President Barack Obama had said earlier that the two sides were working hard on the sidelines of the G-20 summit in China to reach a deal on a cessation of hostilities in Syria.
Obama was speaking at a joint press conference with British Prime Minister Theresa May on the sidelines of the G-20 summit.
Obama noted that the US and Russia have deep differences with regard to the parties they support in Syria as well as the process to bring peace there.
Yet, Obama said the Russian-American talks are key for efforts to reduce violence in the Arab state.
The US president said talks on the situation in Syria are difficult, because trying to corral all forces on the ground into a coherent structure for negotiations is difficult.
Syria has been gripped by foreign-backed militancy since March 2011. United Nations Special Envoy for Syria Staffan de Mistura estimates that over 400,000 people have been killed in the conflict.
The Takfiri terrorists operating in the Middle Eastern state have suffered major setbacks over the past few months as the Syrian army has managed to liberate many key areas.