Former US presidential candidate John McCain said the beheading of journalist James Foley should serve as a turning point for Barack Obama's deliberations on how to deal with Islamic State militants.
"I don't think there's any doubt that this horrible video on the internet is bound to have an impact on the American people," McCain told Reuters.
"The nature of the brutality of this organisation has been brought home by this."
The Republican senator called for a dramatic increase in air strikes against Islamic State targets in Iraq and suggested they should extend into Syria, saying, "We have to defeat them, not stop them."
A British family have told ITV News of their devastation after discovering a close relative is fighting with the Islamic State in Iraq.
A French journalist who was held hostage with James Foley in Syria has told ITV News it was "devastating" to see his murder.