Western countries and Israel have expressed fears chemical weapons could fall into the hands of militant groups as Assad’s authority erodes.

Israel has said that if Syrian-backed Hezbollah guerrillas used the situation to take control of the weapons, it would “act immediately and with utmost force.”

“We’re monitoring that situation very carefully. We have put together a range of contingency plans,” Obama said when asked whether he envisioned the possibility of using U.S. forces at least to safeguard Syria’s chemical arsenal.

The Global Security website, which collects published intelligence reports and other data, says there are four suspected chemical weapons sites in Syria: north of Damascus, near Homs, in Hama and near the Mediterranean port of Latakia. Weapons it produces include the nerve agents VX, sarin and tabun, it said, without citing its sources.

Obama also used the opportunity to renew his call for Assad to step down.

“The international community has sent a clear message that rather than drag his country into civil war, he should move in the direction of a political transition,” Obama said. “But at this point, the likelihood of a soft landing seems pretty distant.”

Obama said the United States had already provided $82 million in humanitarian assistance for Syria refugees and “we’ll probably end up doing a little bit more” to keep the situation from destabilizing Syria’s neighbors.

(Additional reporting by Alister Bull; Editing by Cynthia Osterman)