The last of Syria's acknowledged stockpile of chemical weapons has been handed over to Western governments for destruction, the organization charged with overseeing the elimination of the weapons said Monday.

The final 8 percent of the 1,300-ton stockpile, which included mustard gas and raw materials for making sarin nerve gas, have been loaded onto Danish and Norwegian ships in the Syrian port of Latakia, said Ahmet Uzumcu, the director general of the Organization for the Prohibition of Chemical Weapons.

Speaking at a press conference in The Hague, Uzumcu acknowledged that it is possible Syria has avoided declaring some part of its arsenal.

"I can't say that Syria doesn't have any chemical weapons anymore," he said. However, he added that is true for any country that his organization cooperates with, and Syria's declared arsenal was close to estimates made by external security analysts and experts.

Syria's government agreed to surrender its arsenal last fall when the U.S. threatened punitive missile strikes after a deadly chemical attack on a rebel-held suburb of Damascus.

Uzumcu said that Syrian government cooperation had been "satisfactory."

Following an investigation last month, an OPCW fact-finding mission found evidence chlorine gas may have been used as a weapon in fighting between rebels and Assad's regime. But an attack on the mission prevented it from inspecting the alleged attack site and reaching conclusions about which side might have used it.

Chlorine is not considered a chemical weapon, though using any toxic material as a weapon is illegal under international law.

The chemical weapons shipped out Monday are being transported to a second ship, the U.S.-owned MV Cape Ray, which is equipped with facilities to render toxic material inert.

Under last year's agreement Syria had until the end of June for the destruction of its chemical weapons, but it has been widely acknowledged that the deadline would not be met.

Wire services