US Secretary of State John Kerry will meet foreign ministers from around the world in Paris on Monday to discuss how to defeat Islamic State (IS) militants.
French President Francois Hollande said the beheading of a British aid worker showed the world must act against IS.
About 40 countries, including 10 Arab states, have signed up to a coalition to help fight IS in Iraq and Syria.
Several Arab countries have offered to take part in air strikes on IS fighters in Iraq, US officials say.
Mr Kerry says he is “extremely encouraged” by promises of military assistance to tackle the militant group.
He spoke after a whirlwind tour of the Middle East to try to drum up support for a plan of action unveiled by US President Barack Obama last week.