Rebel groups Sunday set a 48-hour deadline for the US and Russian sponsors of a February ceasefire in Syria's conflict to halt a regime offensive in the Damascus area.

"We are giving the sponsors of the ceasefire 48 hours to rescue what remains of the accord and to force the criminal regime of (President Bashar al-) Assad and his allies to completely and immediately halt their brutal offensive against Daraya and Eastern Ghouta," 29 rebel groups said in a joint statement.