British police say four men from Sri Lanka have been arrested on suspicion of belonging to a banned extremist organisation.
Police said on Friday night they are suspected of violating the Terrorism Act.
The four men are being questioned at a police station in Bedfordshire northeast of London.
Police say the men arrived on an international flight at Luton Airport Wednesday night.
The men have not been identified and have not been charged. Police say the investigation is continuing.
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