“Apologists” for those who commit acts of terrorism are partly responsible for the violence, Philip Hammond has said.
Security services have been criticised over their handling of Mohammed Emwazi – known as “Jihadi John”.
But in a speech the foreign secretary praised the “brilliance” of Britain’s intelligence officers.
Mr Hammond also warned of Russia’s “aggressive behaviour”, saying it could “pose the single greatest threat” to the UK’s security.
Gathering intelligence on Russia’s intentions would be a “vital part” of the work of Britain’s intelligence agencies for the “foreseeable future”, he added.