Syria, ISIS responsible for chemical weapons attacks, UN inquiry finds

Syrian government troops and ISIS terrorists carried out chemical attacks in the war-torn nation during 2014 and 2015, according to an investigation by the United Nations and a global chemical weapons watchdog.

The so-called Joint Investigative Mechanism (JIM) found that forces loyal to Syrian President Bashar al-Assad were responsible for two chlorine attacks in Idlib governorate, one in Talmenes on April 21, 2014 and one in Sarmin on March 16, 2015. And it said ISIS was "the only entity with the ability, capability, motive and the means to use sulfur mustard" gas in Marea in Aleppo governorate on Aug. 21, 2015.

The JIM said three other cases it investigated pointed toward government responsibility but weren't conclusive and three more cases were inconclusive. It called for further investigations in several instances.

The report does not attribute blame for the August 2013 sarin attack on the Damascus suburb of Ghouta that killed hundreds of civilians. The attack came a year after President Obama had said that the use of chemical weapons by Assad's forces would cross a "red line."

"The international community must act to hold accountable those who act in defiance of such fundamental international norms," U.S. Ambassador to the U.N. Samantha Power said in a statement. "It is essential that the members of the Security Council come together to ensure consequences for those who have used chemical weapons in Syria."

In September 2013, Assad agreed to turn over all of its chemical weapons stockpile for destruction under the terms of a deal brokered by the U.S. and Russia. However, Western intelligence officials say Damascus has not turned over "every single bit" of its chemical arsenal as required by the agreement.

After the deal was agreed to, the U.N. Security Council passed a resolution saying that in the event of non-compliance, "including ... any use of chemical weapons by anyone" in Syria, it would impose measures under Chapter 7 of the U.N. Charter.

In the intervening months, Russia and China have used their Security Council veto to protect the Assad government from further U.N. action, including referrals to the International Criminal Court.

Fox News' Jonathan Wachtel and The Associated Press contributed to this report.