Arab leaders have demanded that Damascus "immediately stops violence and murder" in a resolution released at the end of a summit in Baghdad.
The Arab League also called on Syrian security forces to "safeguard Syria's stability" and rejected any foreign military intervention.
The resolution approved at a gathering in Baghdad's green zone called on the "Syrian government and all opposition factions to deal positively with United Nations envoy Kofi Annan by starting serious national dialogue."
It also called on the Syrian opposition "to unify its ranks and prepare to enter into serious dialogue" with Syrian President Bashar Assad, while emphasising that Damascus "should immediately stop all actions of violence and killing."
Iraqi PM Nouri al-Maliki used his speech at the summit to warn against arming either side in the complex conflict.
"Based on our experience in Iraq, the option to arm either side of the conflict will lead to a regional and international proxy war in Syria," Mr Maliki warned.
"This option will prepare the ground for foreign military intervention in Syria."
The Syrian government has pledged to spare no effort to make Mr Annan's peace plan a success, but is demanding that insurgents egged on by Gulf autocracies and their Western allies commit to halting violence.
In brazen attacks, gunmen kidnapped a high-ranking military pilot outside Damascus and assassinated two army colonels in the country's business hub on Thursday.
Chinese Foreign Ministry spokesman Hong Lei urged "Syria's opposition" on Friday to "make responses as soon as possible to create conditions for opening dialogue and stopping violence."