US President Barack Obama insisted Sunday he would press ahead with a visit to Paris for climate talks, calling on world leaders to make a similar show of resolve.

"I think it's absolutely vital for every country, every leader, to send a signal that the viciousness of a handful of killers does not stop the world from doing vital business," he said.

"In addition to hunting down terrorists, in addition to effective intelligence, in addition to missile strikes and in addition to cutting off financing and all the other things that we're doing, the most powerful tool we have to fight ISIL is to say that we're not afraid."