An American company has completed the destruction of the last of Syria's declared chemical weapons stockpile.

The Organization for the Prohibition of Chemical Weapons says in a statement that U.S. firm Veolia destroyed the last 75 cylinders containing hydrogen fluoride at a facility in Texas.

OPCW spokesman Malik Ellahi said Tuesday the destruction had been delayed because some cylinders were badly corroded.

OPCW Director-General Ahmet Uzumcu has welcomed the milestone but adds that the watchdog is continuing efforts to "address ongoing use of toxic chemicals as weapons" in Syria and is still checking the accuracy of the declaration detailing its chemical arsenal made by Damascus when it joined the organization in 2013.

Destruction of the most dangerous elements of Syria's declared arsenal was completed last August.