UN inspectors are investigating seven alleged chemical weapons attacks in Syria - three of which happened after the 21 August Damascus incident that sparked threats of US military action.
The UN said its team of inspectors is set to finish its work by Monday.
The day after, a separate team is due to arrive in Damascus to inspect Syria's chemical weapons stockpile.
That visit, by the Organisation for the Prohibition of Chemical Weapons (OPCW), is due to be formally approved later.
The OPCW's 41-nation executive council will vote on a draft agreement for the inspections on Friday evening.