A 27-year-old man has been arrested in Barking in connection with the London Bridge attack, Scotland Yard has said.
He is being held under the Terrorism Act.
On Monday, all 12 people arrested by officers investigating the attack were released without charge.
Seven women and five men were arrested in Barking on Sunday following the atrocity on Saturday night, which left seven dead and 48 injured.
It comes as the third jihadi attacker has been named as Youssef Zaghba, of Moroccan and Italian nationality.
The Metropolitan Police has previously identified attackers Khuram Butt, a 27-year-old British citizen born in Pakistan, and Rachid Redouane, who claimed to be Moroccan-Libyan.
Butt was known to the security services, but there was no evidence of "attack planning" by him, according to Scotland Yard.
All three attackers were shot dead at the scene of the attack within eight minutes of the first 999 call.
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