Britain’s counter-terrorism police arrested five men, including four Iranian nationals, on suspicion of terrorism offenses, the Metropolitan Police said in a statement on Sunday.

The arrests occurred on Saturday in Swindon, west London, Stockport, Rochdale and Manchester and were related to “a suspected plot to target a specific premises.”

The police did not disclose details of the plot, citing operational reasons.

The Embassy of Iran in London did not immediately respond to a request for comment.

“The investigation is still in its early stages and we are exploring various lines of enquiry to establish any potential motivation as well as to identify whether there may be any further risk to the public linked to this matter,” said Commander Dominic Murphy, head of the Met’s Counter Terrorism Command.

The men aged between 29 and 46 were arrested on suspicion of “preparation of a terrorist act” and remain in custody, police said.

The nationality of one of the men is still being established, they said.

“This is a fast-moving investigation and we are working closely with those at the affected site to keep them updated,” Murphy said.