(CNN) All of the chemical weapons declared by the Syrian regime have been destroyed, according to the Organisation for the Prohibition of Chemical Weapons.

"This process closes an important chapter in the elimination of Syria's chemical weapon programme as we continue efforts to clarify Syria's declaration and address ongoing use of toxic chemicals as weapons in that country," Ambassador Ahmet Üzümcü, the director-general of the OPCW, said Tuesday.

A deal to remove chemical weapons from the war-torn nation was struck in 2013, after video footage appeared to bolster claims by opposition forces that Bashar al-Assad's regime used chemical weapons in an attack on civilians.

U.S. President Barack Obama had said that the use of chemical weapons in the Syrian conflict constituted a "red line" that, if crossed, would force him to reconsider whether or not the United States should intervene in that country's civil war.

Washington eventually agreed to a Russian proposal to remove and destroy the chemical weapons in Syria.