Two men have been arrested at Manchester Airport on suspicion of terrorism offences, while a third was detained in a nearby town, police said on Friday.
The men, who have not been named, were held after a joint operation between Lancashire Constabulary and the Greater Manchester Counter-Terrorism Unit. The third man was arrested in Accrington, Greater Manchester.
Specialist officers have begun searching their houses in Blackburn. They were held under anti-terrorism laws on Thursday.
Police gave no details of those held or why they were arrested.
In a statement, Lancashire Constabulary's Chief Superintendent Andy Rhodes said: "(We) 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 enquiries can be complex and may take time to resolve."
The three men are Asian and aged in their early 20s, according to media reports. The airport's operations were not affected. No one was available to comment at Manchester Airport.