Chemical Weapons have been used — again — in Syria.

A report transmitted to the Security Council yesterday by a the UN-backed Joint Investigative Mechanism (JIM) of the Organization for the Prohibition of Chemical Weapons found several instances of chemical weapons use, including by the Syrian government.

According to the report, obtained by The Associated Press, the JIM found the Syrian government responsible for two chlorine attacks in Idlib governorate, one in Talmenes on April 21, 2014 and one in Sarmin on March 16, 2015.

It also said the Islamic State group was “the only entity with the ability, capability, motive and the means to use sulfur mustard” gas in Marea in Aleppo governorate near the Turkish border on Aug. 21, 2015. At the time, Islamic State fighters were attacking rebels.

The JIM said three attacks indicated possible government involvement — in Kfar Zita in Hama governorate on April 18, 2014, and in Qmenas on March 16, 2015 and Binnish on March 24, 2015, both in Idlib governorate. It said all three need further investigation.

This was not supposed to happen. A Security Council resolution passed in the wake of a chemical weapons attack that killed over 1,000 people in the summer of 2013 mandated that all chemical weapons be shipped out of Syria, and warned of consequences if these weapons were used again.

The Organization for the Prohibition of Chemical Weapons moved quickly, and under significant pressure from the international community–including Russia–Syria’s chemical weapons stockpiles were moved out of the country. The speed and efficiency with which some of the world’s deadliest weapons were removed from the world’s deadliest conflict earned the OPCW a Nobel Peace prize that year.  It was a rare moment of international cohesion in the service of protecting a longstanding international norm against the use of chemical weapons.

Except that some chemical weapons appear to have been hidden from inspectors.

Now what?

A key debate around the 2013 Security Council resolution was what to do in the event of non-compliance. The USA, UK and France preferred to have an automatic trigger that would impose sanctions or other punitive measures in the event of non-compliance. The Russians did not. The final compromise is found in the last line of the resolution which promises to impose “measures under Chapter VII” —  which could include anything from sanctions to military intervention — in the event of non-compliance. (Invoking Chapter VII of the UN Charter permits the Security Council to authorize military strikes, sanctions, and other extreme measures to uphold international peace and security.)

The last line of the 2013 resolution reads:

Decides, in the event of non-compliance with this resolution, including unauthorized transfer of chemical weapons, or any use of chemical weapons by anyone in the Syrian Arab Republic, to impose measures under Chapter VII of the United Nations Charter;

So now, with clear evidence that both the Syrian government and ISIS have used chemical weapons, a showdown is looming between Russia and the West over whether to impose punitive measures on the Syrian government and, if so, what those measures would entail.  A meeting is set for August 30. As of now, it is not at all clear that Russia will abandon the Syrian government. In the five and a half years since the start of the Syrian civil war, Russia has yet to accede to any punitive measures favored by the USA, France and the UK. It’s blocked western lead efforts to impose sanctions and asset freezes on regime officials, and to refer the case to the ICC.

There is nothing to suggest that this latest proof of chemical weapons use by the Syrian government will change Moscow’s diplomatic calculus in any meaningful way.