Two people have been arrested under the Terrorism Act after police executed warrants in Greater Manchester.
No armed officers were involved in the operation
Some 250 officers were involved in the operation - part of the Operation Bracco anti-terrorism initiative.
Eight addresses in the Tonge Moor, Halliwell and Great Lever areas of Bolton are said to have been raided.
A Greater Manchester Police spokeswoman said the arrests were not linked to any other investigation and that none of the officers involved was armed.
Assistant Chief Constable Dave Jones said: "We believe that the action taken today was absolutely necessary to minimise any risk to communities at home and abroad.
"The arrests have been made after careful planning and are part of an ongoing investigation.
"We have been liaising with community representatives to ensure the operation has been carried out with the minimum impact on local people."
People living in nearby communities will be able to discuss issues or concerns linked to Tuesday's operation with local officers, who are providing a high-profile presence.
Officers are also distributing letters around the area and will be meeting with community groups.
A police spokeswoman said the arrests "were targeting individuals suspected of possession of information that could be used for a terrorism purpose."
About 50 officers were directly involved in searching the raided properties.