British police on Sunday said they had arrested five men, including four Iranians, on suspicion of "terrorism offences".

The arrests were carried out in London, Swindon and the Greater Manchester area and were related to "a suspected plot to target a specific premises", London's Metropolitan Police said in a statement.

The men aged between 29 and 46 were arrested on suspicion of "preparation of a terrorist act" and remain in custody, the 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," said Metropolitan Police counter-terrorism chief Dominic Murphy.

"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," he said.