US Secretary of State John Kerry said Tuesday the August 1 date set for Syria's warring parties to agree the framework of a political transition is a "target" not a deadline.

Under the terms of the peace plan agreed by the UN Security Council, Bashar al-Assad's regime and his opposition had until August to agree the outlines of a political process.

But, speaking after a meeting of the International Syria Support Group, Kerry said: "The August date is not a drop date, it's a target date, and we all recognise that if we make significant progress and we're moving we will respect that process."