Counter-terrorism detectives have been granted more time to question four men arrested on suspicion of spying for Iran on locations and individuals linked to the Jewish community.
The suspects, one Iranian and three dual British-Iranian nationals, can now be held in custody until 13 March, the Metropolitan police said on Saturday.
The men, aged 22, 40, 52 and 55, were arrested under the National Security Act at addresses in Harrow, Watford and Barnet shortly after 1am on Friday.
The Met said six other men, aged between 20 and 49, arrested at the same location in Harrow, have been bailed pending further investigation.
One of the men was further arrested on suspicion of assaulting a police officer, the force added.
Detectives are understood to be investigating why the alleged surveillance of Jewish locations and individuals was being carried out and whether it was linked to a wish to carry out attacks on British soil.
Part of the investigation is looking at claims that in-person surveillance in London took place and whether it was directed from overseas. The operation by counter-terrorism police and MI5 had been going on for months.
Shabana Mahmood, the home secretary, said on Friday the arrests meant police had kept “Britain safe from a potential threat”.
Mahmood said: “I want to thank the police and our security services for the action they’ve taken today to keep Britain safe from a potential threat.
“The Jewish community and the wider public will understandably be concerned by today’s arrests. We continue to monitor the situation closely and engage with those affected.”
She added: “I can reassure you that our police and security services are world-leading and won’t hesitate to take action to counter any threat to the UK. They will continue to use the full range of tools and powers available to them to keep this country safe. They have the government’s full support as they carry out their vital work.
“We must now give them the time and space to continue their investigations.”
In October last year, MI5’s director general, Ken McCallum, said 20 plots linked to Iran had been disrupted on UK soil in the previous 12 months. Most of those were against Iranian dissident targets, with at least one linked to an Israeli target in Britain.
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