LONDON, England (CNN) -- Three men arrested by British police on terrorism charges were planning to join an aid convoy to Gaza, a police spokeswoman told CNN Sunday.
Police seized three vehicles and nine men Friday night. Six suspects were released without charge, but police have been granted court permission to hold the other three for questioning until Thursday.
The men were arrested on suspicion of planning to commit terrorist offenses overseas, police and counter-terrorism officials said Saturday.
The men were arrested Friday night under the Terrorism Act on a highway south of the city of Preston, police in England's Lancashire county said.
What the men were planning was not linked to any imminent domestic threat, said Stefan Jarmolowicz, spokesman for the North West Counter Terrorism Unit. But he added, "we don't arrest people under the Terrorism Act lightly."
The cargo in the vehicles is now being searched, Lancashire police said in a statement. No details were released about the contents of the vehicles.
Pictures of the vehicles seen in British media showed them covered in pro-Palestinian posters. The vehicles were heading to London to participate in British MP George Galloway's Gaza aid convoy leaving London on Saturday, a Lancashire police spokeswoman said. She declined to be named in accordance with policy.
Police have not officially notified the convoy organizers of the names of the people who were arrested, so the organizers could not confirm the suspects were registered to participate, Rob Hoveman, a spokesperson for the Gaza operation, told CNN.
"It is, however, my understanding that those six men who have now been released will be trying to join up with the convoy. We are also very concerned if those still in custody actually were going to participate in the convoy and what will happen with them now," Hoveman said.
The arrests are part of an ongoing intelligence-led investigation by Lancashire police and the North West Counter Terrorism Unit, which is run by the nearby Greater Manchester Police, officials said. The arrests were based on intelligence from international agencies such as Interpol, Jarmolowicz said.
CNN's Per Nyberg contributed to this report.