© unknownThe operation is said not to be in connection with this month's London Olympic Games
A 30-year-old woman detained in west London on Thursday, when five men were also arrested, was freed on Saturday.
A 22-year-old woman became the seventh person arrested in the operation when she was detained in east London in the early hours of Saturday.
The arrests are on suspicion of the commission, preparation or instigation of acts of terrorism.
On Friday, a magistrate granted detectives additional time until 12 July to keep in custody those arrested the day before.
The woman and a 21-year-old man were detained at separate addresses in Ealing, while a 29-year-old man was arrested in an Ealing street. The woman is married to one of the men.
The three other men - brothers aged 18, 24 and 26 - were detained in Abbey Road, in Stratford, east London, during an operation involving armed officers.
One of the six was Tasered by police.
Police continue to hold the five men, and the woman arrested later in Hackney, east London, at a south London police station.
Eight homes in west, east and north London and one business have been searched.
YouTube video
It is understood the arrests relate to a possible plot involving Islamist extremists, with potential UK targets.
The BBC understands that the three brothers are Jahangir, Mohammed and Moybur Alom, one of whom is an ex-police community support officer.
He served with the Metropolitan Police for more than two years before resigning in September 2009.
The force said he had not been "deployed in any specialist or sensitive roles".
Richard Dart, a Muslim convert who uses the name Salahuddin al Britani, was also detained in Thursday's raids, it is understood.
He features in a YouTube video which criticises the Royal Family and British military action in Muslim countries.
The Metropolitan Police said the operation was not connected with the Olympics or Paralympics.
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