Jen Psaki, a spokeswoman for the State Department, told reporters in response to questions about the reports on Monday: “Obviously, there needs to be an investigation of what’s happened here. We’re working with our partners to determine what the facts are on the ground.”

The declaration of progress in purging Syria’s chemical stockpile was made by the Organization for the Prohibition of Chemical Weapons, a group in The Hague that is collaborating with the United Nations to oversee compliance with the Syrian government’s promise. The organization’s report came a little more than two months before all of Syria’s chemical arms must be destroyed, under a Security Council resolution.

In a statement posted on its website, the organization said the 17th consignment of the Syrian government’s stockpile had been delivered to the Mediterranean port of Latakia, where it was immediately loaded onto cargo ships and removed from the country.

“This latest consignment is encouraging,” the organization’s director, Ahmet Uzumcu, said in the statement. “We hope that the remaining two or three consignments are delivered quickly to permit destruction operations to get underway in time to meet the midyear deadline for destroying Syria’s chemical weapons.”

Syria’s government committed to the destruction of its chemical weapons under a deal negotiated by the United States and Russia after an Aug. 21 chemical weapons attack in a suburb of Damascus. The government and insurgent groups blamed each other for that attack, in which a United Nations investigative panel said the deadly nerve agent sarin had been used.

Under the Security Council resolution, Syria promised that all of its chemical weapons would be destroyed by June 30, but it failed to meet at least two deadlines this year. Under pressure from the United States and other countries, the Syrians began to expedite the exports and promised that they would be completed by this Sunday.

Mr. Uzumcu said that with the latest shipment, 86.5 percent of the total supply had been removed, including 88.7 percent of the most dangerous compounds, known as Priority 1 chemicals.