Key Syrian rebel groups vowed on Monday to strike back against alleged regime ceasefire violations, casting doubt on the future of fragile peace talks due to resume in Geneva.
A truce agreed in February dramatically curtailed violence across much of Syria, but fighting has surged in recent days around second city Aleppo, causing tens of thousands to flee.
"After the increase of violations by regime forces that included targeting displaced people and continuous bombing of residential neighbourhoods, we declare the start of the battle in response," said a statement signed by 10 armed rebel groups.
In Geneva, where regime and opposition delegations were set to restart indirect negotiations, Syria's main rebel delegation warned that renewed fighting could scupper peace talks.