Obama pledged that justice would be done to the Islamic State (IS) killers of 31-year-old reporter Steven Sotloff, wherever they hid and however long it took.
But he warned that eliminating the threat posed to the region by the group from its bases in Iraq and Syria would take time.
IS posted video footage on the Internet of Sotloff's beheading, confirmed as authentic by Washington, which sparked outrage around the world.
AFP