British police arrested five people last week as part of an investigation which a security source said was linked to the attacks in Paris and Brussels. Four were arrested in Birmingham, central England, and one at London's Gatwick Airport.
West Midlands Police said in a statement that four people, three men and one woman, were still being questioned after securing warrants of further detention, while a 59-year-old man had been bailed "with strict conditions".
"The arrests were pre-planned and intelligence-led. There was no risk to the public at any time and there is no information to suggest an attack in the UK was being planned," said Assistant Chief Constable Marcus Beale, who leads on counter terrorism for the West Midlands.
British media have reported that Belgian Mohamed Abrini, suspected of involvement in the Islamic State attacks in Brussels, had travelled to Birmingham last year and taken photos of a soccer stadium.
Abrini, who investigators say has confessed to depositing a bomb at Brussels airport, is also wanted in connection with the Paris attacks.
Abdelhamid Abaaoud, the suspected planner of the Paris attacks who was killed by French police late last year, is also reported by local media to have visited Birmingham and had photographs of places in the city on his smartphone.