Syria's military and its Russian allies resumed airstrikes on rebel-held areas in the south of the country on Wednesday after rebels said talks over a peaceful government takeover had failed.
The assault targeted areas in and around the provincial capital Deraa, which borders Israel and Jordan.
The rebels had been negotiating with the Russians since Saturday, but said they could not agree to Russia's demands of handing over their heavy weapons in one go.
They want to give up their weapons in stages after tens of thousands of displaced people return home.
Jordan, where most of the refugees are seeking asylum, has urged the rebels to go back to the negotiating table.
Jordan's foreign minister also met with his Russian counterpart Sergei Lavrov in Moscow on Wednesday, urging for a ceasefire.
Lavrov said the matter will likely be discussed at the upcoming U.S.-Russia Summit.