A second man has been released without charge after four men were arrested as part of a counter-terror investigation relating to Iran.

The Metropolitan Police said a 52-year-old, who was arrested in Watford, was released on Sunday.

The four suspects, one Iranian and three dual British-Iranian nationals, were arrested on 6 March under the National Security Act on suspicion of assisting a foreign intelligence service.

The Met previously said the investigation related to the suspected surveillance of locations and individuals linked to London's Jewish community.

A 55-year-old man, who was arrested in Barnet, has also been released without charge.

The two remaining suspects, aged 22 and 40, remain in custody.

Investigators have permission to hold them in police custody until 20 March.

As part of the operation, six other men were arrested on suspicion of assisting an offender, with one further arrested on suspicion of assaulting a police officer.

All six have been bailed pending further inquiries.

Commander Helen Flanagan, head of Counter Terrorism Policing London, previously said the arrests were part of "a long-running investigation" and "ongoing work to disrupt malign activity where we suspect it".