ShareSaveShareSavePA MediaPolice conducted searches on FridayDetectives have been given until 13 March to question four men detained as part of a counter-terror investigation relating to Iran.
The suspects, one Iranian and three dual British-Iranian nationals, were arrested on Friday on suspicion of assisting a foreign intelligence service.
The Metropolitan Police previously said the investigation related to the suspected surveillance of locations and individuals linked to London's Jewish community.
On Saturday, the force said it had "secured warrants of further detention" for the four men under the National Security Act.
They are a 40-year-old and 55-year-old arrested in Barnet, a 52-year-old arrested in Watford, and a 22-year-old arrested in Harrow.
Six other men have been bailed pending further investigation, the Met said.
The six men, aged from 20 to 49, were arrested at the same location in Harrow on suspicion of assisting an offender. One was also arrested on suspicion of assaulting a police officer.
