U.S. President Barack Obama Monday warned Syrian President Bashar Al-Assad that his use of chemical weapons in the conflict there would be "totally unacceptable" and that he would be "held accountable." "I want to make it absolutely clear to Assad and those under his command, the world is watching," Obama said at the Nunn-Lugar Cooperative Threat Reduction symposium in Washington. "The use of chemical weapons is and would be totally unacceptable. And if you make the tragic mistake of using these weapons, there will be consequences, and you will be held accountable," Obama said. "We will continue to support the legitimate aspirations of the Syrian people, engaging with the opposition ... providing them with humanitarian aid and working for a transition to a Syria that's free of the Assad regime," Obama said.