International weapons inspectors have issued preliminary findings that chlorine gas was used in a “systematic manner” in Syria this year, long after the government of President Bashar al-Assad pledged to give up other toxic weapons such as sarin.

The Organization for the Prohibition of Chemical Weapons (OPCW) mission said this week that evidence “lends credence to the view that toxic chemicals, most likely pulmonary irritating agents such as chlorine, have been used.”

The OPCW investigation followed French and U.S. allegations that Assad’s forces may have used industrial chemicals against rebel-held areas this spring.

The agency also said that a deadline to remove Assad’s declared stockpile of chemical weapons from Syrian soil is unlikely to be met. International inspectors have removed about 92 percent of the declared material, including sarin, but have not been able to get the necessary cooperation and clearances to extract the final 8 percent.

“Ongoing delays in transporting the remaining 8 percent of chemicals mean that Syria will miss the target date of June 30 for the complete destruction of its chemical weapons program,” said OPCW Director General Ahmet Uzumcu.

The Obama administration has not decided what action, if any, it might take in reaction to the preliminary evidence cited by the OPCW, State Department spokeswoman Jen Psaki said Wednesday.

“We will evaluate” the final conclusions before deciding whether Syria had again crossed President Obama’s “red line” that chemical warfare is intolerable, Psaki said. She would not speculate about any U.S. action that might follow.

The U.S. representative to the OPCW blamed Syria and suggested this week that the international body get much tougher on the Assad regime.

“It was certainly the expectation of the United States and other members of the council that the elimination of Syria’s entire chemical weapons program would be completed by June 30, 2014,” Robert Mikulak said in a statement.

“Syria has deliberately frustrated the council’s efforts to complete destruction by June 30,” he said. “The council will need to acknowledge that Syria has not met its obligations to remove these dangerous materials so that they can be destroyed.”

The Obama administration forcefully condemned use of sarin gas by Assad’s forces last summer and prepared for airstrikes in Syria before referring the matter to Congress.

Syria then agreed to give up its chemical weapons, which it had previously denied existed, with the understanding that U.S. airstrikes would then be highly unlikely.

The sarin nerve gas attack in a rebel-held Damascus suburb killed more than 1,000 people last summer.

An OPCW team went to Syria to probe the new allegations of chlorine use. Chlorine has many peaceful uses but can be deployed in gas form as a chemical weapon, and such use is banned under an international treaty. Syria did not have to declare chlorine as part of its agreement to give up chemical weapons.

The investigating team was attacked with a roadside bomb and gunfire on May 27, preventing inspectors from reaching the site of an alleged attack in the village of Kfar Zeita, the preliminary report said.

“The attack on the team and the resulting denial of access prevents it from presenting definitive conclusions,” the report said, according to news agencies.

Despite not being able to visit the site of the alleged chlorine attack, OPCW officials spoke to doctors in Kfar Zeita “and obtained their verbal medical reports relating to the treatment of individuals allegedly affected by exposure to chlorine,” Agence France-Presse reported.

The team also saw video footage of the alleged attack and of alleged munitions used in the attack, some of which remained intact.