The most dangerous material will be transferred to an American ship, which will move into international waters and use specialized equipment to destroy the chemicals over the next two months. Other material will be disposed of at toxic waste sites in various countries.
Questions persist over whether Syrian President Bashar Assad is hiding undeclared poison gases or attacking rebels with chlorine — a toxic industrial gas that is not specifically classified as a chemical weapon.
But politicians and activists hailed Monday's milestone as a victory for international diplomacy, and, at the least, a clear reduction in the amount of chemicals available for use in Syria's bloody civil war.
The news came amid extremely high tension across the Middle East, as Israel carried out retaliatory strikes on Syria and a Syrian cabinet member warned that Sunni insurgents in Iraq have been funneling weapons to rebels in Syria.
The material includes mustard gas and precursors to the nerve gas sarin.
Syria agreed to surrender its arsenal when the U.S. threatened missile strikes in retaliation for a chemical attack on a rebel-held suburb of Damascus. The attack is believed to have killed more than 1,000 people.
The deal was put together by the United States and Russia, which has been Assad's most powerful international backer during the war.
The Organization for the Prohibition of Chemical Weapons, the watchdog agency overseeing Syria's disarmament, confirmed that the final 100 tons of chemicals had been loaded onto a Danish ship in the Syrian port of Latakia.
The completion of the task came nearly two months past the April 27 deadline set by the United Nations. The OPCW said that was because of security concerns amid the fighting.
"The last thing you want, of course, is when you're dealing with chemical weapons elimination, that chemical weapons material falls into the wrong hands," Sigrid Kaag, head of the joint U.N.-OPCW mission in Syria, said at the project's staging ground in Cyprus.
Ahmet Uzumcu, director general of the OPCW, acknowledged that Syria could still be hiding some of its arsenal.
"I can't say ... that Syria doesn't have any chemical weapons anymore," Uzumcu said.
But he said that that was true of any country that his organization works with. And he added that Syria's declared arsenal was close to estimates made by outside experts.
He described the Syrian government's overall cooperation as "satisfactory."
Kaag said her team's experts "are working closely with the Syrian Republic to look at any discrepancies or any revisions" in Syria's declaration that need to be made.
Others applauded the move.
"To its great credit, the OPCW, the United Nations, the United States, Russia and a diverse coalition of more than two dozen states stepped up to the unprecedented task of verifiably removing a country's entire chemical weapons stockpile under tight deadlines and wartime conditions," said Daryl Kimball of the Washington-based Arms Control Association.
During a visit to Baghdad, U.S. Secretary of State John Kerry said the step was significant step toward diminishing the threat of chemical warfare in the region.
But he warned that the use of chlorine gas remains a serious issue amid the three-year war in Syria that has claimed an estimated 160,000 lives.
"We are always going to remain truly appalled at the level of death and destruction that continues to consume Syria, notwithstanding the removal of these weapons," he said.
An OPCW fact-finding mission last month found evidence that chlorine gas was used in fighting between rebels and Assad's government. The OPCW stopped short of saying which side was to blame.
The use of any toxic material as a weapon is illegal under international law.
The Syrian Foreign Ministry said in a statement that the removal of the chemicals "is further evidence that Syria adheres to its international commitments."
Louay Safi, a senior member of the rebel Syrian National Coalition, said he is skeptical Syria has declared all its chemical weapons.
"We know that even after Syria signed the chemical weapons agreement it used chlorine," he said.
Some of the handed-over chemicals will be transferred to the U.S.-owned ship MV Cape Ray, which has sophisticated machinery that will essentially use water to break down the toxic material into less dangerous substances.
Andrew Tabler, a senior fellow at the Washington Institute for Near East Policy, agreed the reduction in arms is a net positive but said now it will become more evident that the U.S. has few good options for helping resolve Syria's complicated conflict.
"The war in Syria was never about chemical weapons. That was just one chapter of it, and it's not completely closed," he said.
Sterling reported from Amsterdam. Zeina Karam and Bassem Mroue in Beirut, Albert Aji in Damascus, Lolita Baldor in Washington, Edith Lederer in New York, and Lara Jakes in Baghdad contributed to this report.
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