International investigators say the destruction of Syria’s chemical weapons production facilities has begun.

The latest report by the Organization for the Prohibition of Chemical Weapons says the destruction of the 12 facilities is expected to be complete by the end of June. The destruction is a key part of the elimination of Syria’s chemical weapons stockpile as ordered by the U.N. Security Council in September 2013.

The OPCW has already reported that all of Syria’s declared chemical weapons have been removed from the country for their destruction, though concerns remain that Syria didn’t declare everything it had.

The OPCW continues to look into allegations of the use of chlorine “for hostile purposes” in Syria.

The United Nations circulated the watchdog’s latest report on Friday.

(AP)