MOSCOW—Despite Syrian president Bashar al-Assad’s flat-out admission to the Russian leader that he was responsible for an August 21 chemical weapons attack on a suburban Damascus neighborhood.

Russian president Vladimir Putin confirmed Wednesday that al-Assad has yet to provide a convincing case that he carried out the assault.

“Given the information I’ve seen at this point, President Assad failed to show me clear, substantiated evidence that he used chemical weapons against the Syrian people, regardless of how many times he says ‘I, Bashar al-Assad, President of Syria, am the one who did this’ while showing me videos of people dying of Sarin poisoning,” said Putin.

Adding that he remains extremely skeptical despite phone conversations in which a reportedly frustrated Assad repeats, over and over again, the step-by-step account of how he authorized the use of nerve gas to kill over 1,400 people.

“We need to know all the facts before we act. I don’t care how many autopsy reports, laboratory tests, or pictures of Assad pressing a button labeled ‘chemical weapons launcher’ he sends me—before we have conclusive proof that he and not the opposition forces did this, we cannot say that Syria is in violation of international law.”

Putin went on to confirm that until Assad proves beyond a doubt that he carried out the alleged attack, Russia will continue delivering components of a surface-to-air missile defense system to the Syrian government