U.S. Secretary of State Mike Pompeo said on Thursday that the United States has concluded the government of President Bashir al-Assad in Syria used chlorine as a chemical weapon during a May battle with insurgents in Idlib, according to the Reuters. “Today I am announcing that the United States has concluded that the Assad regime used chlorine as a chemical weapon on May 19,” Pompeo told reporters in New York. “The Assad regime is responsible for innumerable atrocities some of which rise to the level of war crimes and crimes against humanity."

The attack took place on May 19 near the village of Kabana. The U.S. government has donated $4.5 million to the Organization for the Prohibition of Chemical Weapons, which investigates chemical weapons use. Syria joined the chemical weapons convention in 2013, which prohibits the development, production, and use of poison gas. The Trump administration has carried out two military strikes against Syrian military facilities in response to its use of chemical weapons, according to The Wall Street Journal.