British police have arrested five people on suspicion of preparing acts of terrorism as part of an investigation which a security source said was linked to the attacks in Paris and Brussels.
Three men and a woman were detained in Birmingham, central England, on Thursday and another man was held at London's Gatwick Airport in the early hours of Friday.
Chief Constable Marcus Beale from West Midlands Police said there was no information to suggest an attack in Britain was being planned.
He added in a statement: "This action forms part of an extensive investigation by West Midlands Counter Terrorism Unit, together with the wider counter terrorism network, (domestic spy agency) MI5 and international partners including Belgian and French authorities to address any associated threat to the UK following the attacks in Europe."
Police declined to give any further details but a security source confirmed the arrests were linked to the suicide bombings in Brussels which killed 32 people last month and November's attacks in Paris which left 130 people dead.
The four men, aged 40, 59 and two aged 26, and the 29-year-old woman are now being questioned by counter-terrorism detectives and police are searching several properties in Birmingham.
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 British newspapers to have visited Birmingham last October and had photographs of places in the city on his smartphone.
Asked about Abaaoud in parliament last month Home Secretary Theresa May said: "This is obviously an ongoing investigation, and we are working very closely with the Belgian authorities to ascertain as much information as possible about the individuals involved."
Separately, the Belgian transport minister resigned on Friday, local media said, after accusations she lied about an EU report that criticised security at Brussels Airport long before last month's bombing.
Public broadcaster RTBF said Prime Minister Charles Michel had accepted the resignation of Jacqueline Galant. Michel had earlier defended the minister, who is from his own centrist party in the coalition government, saying her office had not been aware of a critical report sent a year ago by EU officials.
Government officials could not immediately be reached for comment. RTBF quoted a spokesman for the centrist MR party saying that documents presented late on Thursday had shown that Galant's office had indeed been informed of the EU report.
On March 22, two Islamic State suicide bombers detonated suitcase bombs in the departure hall of Brussels Airport before a third struck a metro train in the city. In all, they killed 32 people.