Opposition member Erin Erdem told the broadcaster RT, on Monday, that components of chemical weapons had been brought to Turkey and subsequently combined in camps held by Islamic State (Daesh in Arabic) in Syria.
"The list of traitors consists [of] those who accuse their own state of selling chemical weapons in interviews with foreign television channels," Erdogan said during an address in Konya. "What is this treachery?"
Erdem's interview with RT came a week after he questioned in parliament why an investigation, which had uncovered wiretapped conversations between Turkish citizens with Daesh representatives about sarin supplies, had been abruptly closed.
The case is alleged to have been closed and all suspects allowed to cross the Turkish-Syrian border a week after it was opened by a prosecutor in the southern city of Adana.
On Wednesday, local media reported that the Republican People's Party (CHP) member was facing charges of treason under criminal investigation for relaying the information.
Sarin is a lethal gas, classified by the United Nations as a weapon of mass destruction. The Syrian government has been blamed for sarin attacks on civilian populations in the past, leading to a UN-brokered deal that saw all precursor chemicals for sarin removed from Syria.