A video posted by rebels on Wednesday showed the bodies of dozens of soldiers executed by a roadside. At least one of them appeared to have been beaten to death. The United Nations and rights group say the military and rebels have both committed war crimes, but have so far placed most of the blame on the army.
Past peace efforts have floundered, with world powers divided over what has become an increasingly sectarian struggle between mostly Sunni Muslim rebels and Assad's security forces, drawn primarily from his Shiite-rooted Alawite minority.
Deputy Foreign Minister Faisal Makdad flew to Moscow to discuss the details of the talks with Brahimi, said a Syrian security source, who would not say if a deal was in the works.
However, a Lebanese official close to Damascus said Makdad had been sent to seek Russian advice on a possible agreement.
He said Syrian officials were upbeat after talks with Brahimi, the U.N.-Arab League envoy, who met Foreign Minister Walid Moualem on Tuesday a day after his session with Assad, but who has not outlined his ideas in public.
"There is a new mood now and something good is happening," the official said, asking not to be named. He gave no details.