The United States gave Israel two hours warning before it fired on a Syrian airbase from which a chemical attack had been launched on Syrian civilians the day before, according to Israeli military officials.

Senior Israeli military officials also told reporters at a briefing Wednesday that Syrian President Bashar Assad still has up to three tons of chemical weapons, despite agreeing to eliminate his country’s stocks of chemical weapons in 2013, the Associated Press reported.

Assad has denied responsibility for the April 4 attack on Idlib, an area in southern Syria held by rebels in the country’s six-year civil war. At least 90 civilians were killed in the attack using sarin gas.

Israel has remained on the sidelines of the civil war, though it has treated Syrian injured, both government troops and rebels, on the border and responded when rocket and artillery fire from the fighting has landed on Israel’s side of the Golan Heights.

In the wake of the attack, Israeli lawmakers from the right and left called for the international community to get involved in Syria’s civil war.