Three Muslim men have been arrested on suspicion of committing terror offences, police say.
Two of the men were held at Manchester Airport, while the third was detained in nearby Accrington.
Lancashire Police said the men, aged 21, 22 and 23, were all from the Blackburn area. Their homes are being searched by specialist officers.
The arrests were a joint operation between Lancashire Police and Greater Manchester Counter Terrorism Unit.
Ch Supt Andy Rhodes, of Lancashire Police, said: "Lancashire Constabulary will investigate any information that is passed to us, and ensure it is accurate, before responding in a proportionate and measured way.
"These arrests and subsequent searches of the nearby premises will be conducted with sensitivity and carried out as quickly as possible to ensure minimum impact on the three areas concerned.
"However, these types of inquiries can be complex and may take time to resolve.
"I would ask local residents to be patient with us and to be assured that we will keep them updated in relation to the investigation as and when we can."
Bill Crawshaw, terminal duty manager at Manchester Airport, said the arrests had no effect on the airport.
"It is a total police operation and we didn't even know that it had happened until afterwards," he added.
Omar Hussain, who lives near the houses being searched in Blackburn, said he had been handed a leaflet by police advising people of the arrests.
He added: "It's really worrying that it's so close. It's like 'oh my God, who is it?' You can't believe it's actually happening on your street, in your community."
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