“The only way you can destroy the caliphate is with a ground component,” said Graham, who is seeking his party’s presidential nomination. “The aerial campaign is not turning the tide of battle.“

McCain, chairman of the Senate armed services committee, recently proposed intervention in Syria by a European and Arab ground force backed by 10,000 US military advisers and trainers.

On Sunday, he and Graham told reporters during a visit to Baghdad that US personnel could provide logistical and intelligence support to a proposed 100,000-strong force from Sunni Arab countries like Egypt, Turkey and Saudi Arabia. Graham said special forces would also be included.