JERUSALEM (JTA) — Israeli Prime Minister Benjamin Netanyahu called Syria “Iran’s testing ground” in the wake of the reported use of chemical weapons against Syrian citizens.

The use of chemical weapons in Israel’s northern neighbor against “innocent civilians” is “terribly disturbing,” Netanyahu said in remarks released by his office on Thursday.

“If verified, it will be a horrible addition to the roster of tragic crimes committed by the Syrian regime against the people of Syria,” the Israeli leader said. “It is absurd that the U.N. investigators, who are right now in Damascus to verify use of chemical weapons, are prevented from reaching the afflicted areas by the Syrian regime.”

It has been reported by Syria’s opposition that up to 1,300 civilians were killed in the alleged chemical attack in the suburbs of Damascus. The Syrian government and the army have denied using chemical weapons.

“Syria has become Iran’s testing ground, and Iran is closely watching whether and how the world responds to the atrocities committed by Iran’s client state Syria and by Iran’s proxy Hezbollah against innocent civilians in Syria,” Netanyahu said. “These events prove yet again that we simply cannot allow the world’s most dangerous regimes to acquire the world’s most dangerous weapons.”

Ban Ki-moon, the secretary-general of the United Nations, called for an international investigation into the incident. The U.N. Security Council issued a call to “clarify” the incident.