Obama warns Assad on chemical weapons

• Obama to Syrian dictator: Don't use chemical weapons
• Says there will be 'consequences' if chemical weapons are used on Syrian rebels
• 'The world is watching,' Obama says

President Obama warned Syrian dictator Bashar Assad on Monday that the use of chemical weapons is "totally unacceptable," and he will be punished if they are deployed against rebel forces.

"The world is watching," Obama said of Assad during a Washington symposium on nuclear non-proliferation. "If you make the tragic mistake of using these weapons, there will be consequences, and you will be held accountable."

He added: "We simply cannot allow the 21st century to be darkened by the worst weapons of the 20th century."

Secretary of State Hillary Rodham Clinton has issued a similar warning to Assad's government.

The warnings come as U.S. officials report that intelligence agencies have detected a movement of chemical weapon components in Syria in recent days.

Addressing the unrest in Syria, Obama said: "We will continue to support the legitimate aspirations of the Syrian people -- engaging with the opposition ... providing them with the humanitarian aid, and working for a transition to a Syria that's free of the Assad regime."

Obama made the comments during remarks at the annual Nunn-Lugar Cooperative Threat Reduction (CTR) symposium at the National Defense University in Washington, D.C.

It is the 20th anniversary of the program designed to track down nuclear weapons and nuclear materials that were unsecured at the end of the Cold War. Obama paid particular tribute to the two leaders who developed the program: Outgoing Sen. Richard Lugar, R-Ind., and retired Sen. Sam Nunn, D-Ga., calling them the very definition of visionaries.

"They look at the world and see what's missing," Obama said. "So they set out to fill the gap."