U.S. officials said Monday that they were behind an airstrike in Syria that killed a leader and spokesman for the al-Nusra Front, an al Qaeda-affiliated militant group. Abu Firas al-Suri—known as “the Syrian”—was a founding member of the terror group. He was reportedly killed Sunday with 20 other fighters, including his son, in northwestern Syria. An official “cessation of hostilities” has existed in Syria for more than a month, while several groups attempt to negotiate an end to the country’s five-year civil war, but that agreement does not include ISIS or al-Nusra. The Syrian Observatory for Human Rights had said earlier Monday that Suri was likely killed by a Syrian or Russian attack.