President Barack Obama says U.S. thinking on possible military involvement in Syria would change if chemical or biological weapons came into play in the Syrian civil war.
Speaking to reporters on Monday, Obama said the use of such weapons of mass destruction, which Syria has, would widen the conflict considerably.
Obama said, quote: "It doesn't just include Syria. It would concern allies in the region, including Israel, and it would concern us."
Obama warned the regime of President Bashar Assad -- and "other players on the ground" -- that the use or movement of such weapons would be a "red line" for the United States.