PARIS (AFP) - US President Barack Obama and his French counterpart Francois Hollande are both convinced the Syrian regime used chemical weapons on its own people last week, an aide to Hollande said on Friday.

The two leaders "share the same certainty that the attack was chemical in nature and that the regime was undoubtedly responsible," the aide said after Obama and Hollande held phone talks on Friday.

"Francois Hollande repeated France's determination not to leave these crimes unpunished and felt the same determination on Obama's side."