The Los Angeles Times reported: President Obama on Thursday ruled out unilateral U.S. military action in Syria even if proof emerges that Syrian forces have used lethal chemical weapons.

“This is … an international problem,” Obama said at a White House news conference with visiting Turkish Prime Minister Recep Tayyip Erdogan. “It’s not going to be something that the United States does by itself. And I don’t think anybody in the region would think that U.S. unilateral actions … would bring about a better outcome.”

Obama’s warnings since August that Syrian President Bashar Assad would cross a “red line” if his forces used poison gas in the nation’s civil war were widely viewed as a trigger for potential U.S. military intervention.

But in recent weeks, with growing evidence indicating use of sarin nerve gas, Obama has made it clear he wants conclusive proof before ordering a response. He previously indicated that he would prefer a collective response, but Thursday was the first time he categorically ruled out action by the United States alone.