Western countries face the prospect of being dragged further into the war in Syria as it prepares to support a newly-formed "ground army" from Muslim nations which could attack Isis within weeks.
The coalition of 34 largely Sunni Muslim nations said it was planning to send special forces into Syria to help defeat Isis (Islamic State).
Nato countries' forces are already bombing Isis in both Iraq and Syria, but military sources said they would have to provide command and control, intelligence and air support to troops from the new coalition.
British military sources said that while the UK would not provide boots on the ground, they were on standby to provide air support and "command and control".
But any Gulf or other forces would clearly add to or take the place of the 70,000 "moderate rebels" whom British Prime Minister David Cameron wants to be the "boots on the ground" to displace Isis in Syria but who say they already have their hands full fighting the Assad regime.
The Saudis and their Sunni Muslim allies would also be intent on preventing any vacuum being filled by the Bashar al-Assad regime, or its Shia Iranian allies, against whom the Gulf is facing off across the region.
That raises the prospect of the West being drawn directly into the confrontation between the two rival sectarian blocs.
Saudi Arabia's powerful new deputy crown prince, Prince Mohammed bin Salman, unveiled the coalition in the capital Riyadh.
"There are discussions, countries that are currently part of the coalition [like] Saudi Arabia, the Emirates, Qatar and Bahrain, about sending some special forces into Syria, and those discussions are ongoing," said Adel al-Jubeir, the Saudi Foreign Minister.
The Gulf states, some of which have been accused of supporting militants, are attempting to prove their loyalty to Western allies and their determination to take on Isis.
Jubeir said the new alliance would share information and train, equip and provide troops.
A 16-month bombing campaign has failed to crush Isis and military planners say victory will require a unified ground force that can hold territory and progress under cover of air strikes.