The United States and European governments are urging tougher international pressure on Syria over a sarin gas attack and stepped-up efforts to find the perpetrators.

The international chemical weapons watchdog OPCW held a special meeting on Wednesday in The Hague, after confirming in a recent report that sarin was used in the April attack on the town of Khan Sheikhoun. The report didn’t say who was responsible for the attack, which killed more than 90 people.

U.S. Ambassador Kenneth Ward says “there should be no doubt” Syria’s government was behind the attack. European delegates strongly condemned the attack, urging Syria to cooperate with the investigation.

Syrian President Bashar Assad denies using chemical weapons. Russia’s Vladimir Putin said he believed the attack was staged by those seeking to blame Assad.

(AP)