The final stockpile of Syria’s chemical weapons has been shipped out of the country, the Organization for the Prohibition of Chemical Weapons said on Monday.

CNN quoted Ahmet Uzumcu, the chief of the international watchdog organization, as having said the weapons were loaded aboard the Danish ship Ark Futura and departed the Syrian port of Latakia.

“A major landmark has been reached today,” Uzumcu said, qualifying that that meant all “declared” weapons were out of the country.

“We cannot say for sure it has no more chemical weapons,” Uzumcu said. “All we can do is work on the basis of verifying a country’s declarations of what they have. I would not make any speculation to possible remaining assets, substances, chemical weapons.”

The international operation to destroy Syria’s stockpile of deadly chemicals is a joint Russian-U.S. plan that was endorsed by the UN Security Council last September. 

The resolution was a last-minute measure to prevent an American strike on Syria in retaliation for the regime’s alleged use of chemical weapons in an attack on a Damascus suburb in August that left hundreds dead.

The Obama administration said at the time that Syria had crossed a “red line” with its use of chemical weapons during the nation’s civil war, which has raged since 2011.

In late April, the OPCW indicated that Syria had nearly completed surrendering its chemical weapons stockpile. That announcement came after Syria missed several deadlines in the plan to move all of its declared chemical substances and precursors out of the country.