Former United States secretary of state John Kerry said in an interview broadcast on Sunday, that he was unable to persuade then-President Barack Obama that Syrian President Bashar al-Assad "needed to be taught a lesson" for violating ceasefires and using chemical weapons on his own people.

Referring to Obama's warning in 2012 that use of chemical weapons would prompt a military response by the US, a threat that was not enforced a year later, Kerry told CBS's Face the Nation, "We paid a price for the way it played out without the red line being enforced by the bombing." He added, "And all the explanations and everything else doesn't change the perception, and perceptions sometimes are very telling in diplomacy and politics."