Wiping out Islamic State (IS) "will not end" the global threat from jihadist groups, according to a report.
At least 15 militias, numbering 65,000 fighters, could fill any vacuum resulting from a defeat of IS in Syria and Iraq by a coalition led by the US, the Centre on Religion & Geopolitics said.
Some 60% of fighters in rebel factions in war-torn Syria identify with a religious and political ideology similar to the terror group, also known as Isis, Isil and Daesh, the report added.
The centre, a think tank run by the Tony Blair Faith Foundation, said: "The West risks making a strategic failure by focusing only on IS. Defeating it militarily will not end global jihadism. We cannot bomb an ideology, but our war is ideological."
The report comes after the United Nations agreed a resolution endorsing the start of "urgent" formal negotiations between president Bashar Assad's regime and moderate opposition groups early next month.
But the centre warned the radical groups, including al Qaida affiliate Jabhat al-Nusra and Ahrar al-Sham, could benefit if they go "unchallenged".
It added: "If Isis is defeated, there are at least 65,000 fighters belonging to other Salafi-jihadi groups ready to take its place.
"The greatest danger to the international community are the groups that share the ideology of Isis, but are being ignored in the battle to defeat the group.
"While military efforts against Isis are necessary, policy makers must recognise that its defeat will not end the threat of Salafi-jihadism unless it is accompanied by an intellectual and theological defeat of the pernicious ideology that drives it."