4 Iranians among 5 arrested in UK for 'terrorism offences': police

British police on Sunday said they had arrested five men, including four Iranians, on suspicion of "preparation of a terrorist act".

The arrests were carried out in London, Swindon and the Greater Manchester area, with all five arrested on suspicion of "terrorism offences", London's Metropolitan Police said in a statement.

The — Reuters — which was not named — and remain in custody.

The nationality of one of the men is still being established, police 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 added.

Meanwhile, three other men, all Iranian nationals, were arrested in London in a separate Counter Terrorism Police operation on Saturday.

The men, aged 39, 44 and 55, were arrested under the National Security Act — which gives law enforcement greater powers to disrupt "state threats" including foreign interference and espionage — the Met Police said in a statement on Sunday.

Interior minister Yvette Cooper "thanked" the police in a statement.

"These are serious events that demonstrate the ongoing requirement to adapt our response to national security threats," Cooper told the PA news agency.

"The Government continues to work with police and intelligence agencies to support all the action and security assessments that are needed to keep the country safe."