A man arrested in connection with the 1974 Birmingham pub bombings which killed 21 people is reported to be Michael Patrick Reilly.
The blasts at the Mulberry Bush and Tavern in the Town pubs on the night of 21 November also injured 220 people.
Police said a man, 65, was held at his Belfast home on Wednesday under Section 41 of the Terrorism Act 2000 and would be questioned in Northern Ireland.
Mr Reilly has strongly denied any involvement in the bombings.
West Midlands Police added the address was being searched and the man was to be interviewed under caution at a police station.
Fresh inquests last year ruled the victims were unlawfully killed, but did not establish who was responsible.
Six men, who became known as the Birmingham Six, were wrongly jailed for the bombings in 1975 following a botched police investigation, but their convictions were quashed by the Court of Appeal in 1991.
Saturday marks the 46th anniversary of the bombings and the arrest comes within a month of an announcement from Home Secretary Priti Patel that she would consider the case for a public inquiry into the attacks.