LONDON — British counterterrorism officers arrested four Iranian men over an alleged plot to attack an unspecified target and three others over a national security threat, police said Sunday. The government called them the biggest “counter state threat and counterterrorism” operations for years.

The Metropolitan Police force said five men aged between 29 and 46 were detained Saturday in various parts of England under the Terrorism Act on suspicion of preparing “a terrorist act.”

Four are Iranian citizens and the nationality of the fifth was still being established.

Police said the attack plot targeted a single location that was not being named “for operational reasons.” It said the premises was being given “advice and support.”

All the suspects were being questioned at police stations and have not been charged. Police said they are searching several properties in London, the Manchester area of northwest England and Swindon in western England.

— The Associated Press