Police have been granted more time to question four men arrested on Friday on suspicion of spying for Iran on locations and individuals linked to the Jewish community.
It means the suspects, one Iranian and three dual British-Iranian nationals, who were arrested under the National Security Act, can be held in custody until March 13.
The men, aged 22, 40, 52 and 55, were arrested at addresses in Harrow, Watford and Barnet shortly after 1am on Friday.
The Metropolitan Police said six other men, aged between 20 and 49, arrested at the same location in Harrow on suspicion of assisting an offender, have been bailed pending further investigation.
One of the men was further arrested on suspicion of assaulting a police officer, the force added.
The Metropolitan Police said on Saturday that detectives from Counter Terrorism Policing London have secured warrants of further detention.
