The findings were presented in the latest monthly report on Syria from chief of the OPCW Ahmet Uzumcu.
According to the report, the mission to Syria was looking into charges by the Syrian government that chemical weapons were used in 11 instances. The report did not specify when the alleged chemical attacks occurred.
"In one instance, analysis of some blood samples indicates that individuals were at some point exposed to sarin or a sarin-like substance. Further investigation would be necessary to determine when or under what circumstances such exposure might have occurred," Uzumcu was quoted as saying by Reuters.
Several sources also reported that chemical materials, particularly the deadly sarin gas, were delivered from Turkey to Syrian militants.
The latest to speak publicly on the allegations was Eren Erdem, a member of the Turkish opposition Republican People’s Party (CHP). In December 2015, he disclosed to RT that Ankara was aware of sarin supplies to terrorist groups via Turkey.
Syria agreed to destroy its entire chemical weapons arsenal in September 2013, under a deal negotiated with the US and Russia after hundreds of people were killed in a sarin gas attack in the outskirts of Damascus.
Sarin is a lethal gas, classified by the UN Resolution 687 as a weapon of mass destruction and banned by the UN Chemical Weapons Convention of 1993. By late October 2014, the OPCW declared that nearly 98 percent of the chemical weapons in Syria had been removed and destroyed.