US secretary of state John Kerry and Russian foreign minister Sergey Lavrov have reached an agreement on a framework for securing Syria's chemical weapons after the third day of intense negotiations in Geneva.

They say some elements of the deal include a timetable and how Syria must comply - and that if Syria fails, they will seek a Security Council resolution that could authorise military action.

At a news conference, Mr Kerry said the pair and their teams of experts had reached "a shared assessment" of the existing stockpile and that Syria must destroy all of its weapons.

Mr Kerry said "we have committed to a standard that says, verify and verify".

The negotiations between the United States and Russia on securing Syria's chemical weapons are considered key to a resumption of peace talks to end the civil war in the country.

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