Police have detained a number of people in early morning raids in east London as part of the investigation into the London Bridge attack.
Seven people were killed and 49 injured on Saturday night when attackers rammed a van into pedestrians on London Bridge before stabbing revellers in bars in the nearby Borough Market.
Isis claimed responsibility for the attack, the third major militant assault to hit Britain in less than three months.
Terrorists brought carnage to the streets of Britain for the second time in as many weeks, killing seven and leaving 21 fighting for their lives.
A Canadian woman, who died in her fiance's arms after being struck by the speeding van, was named as 30-year-old Christine Archibald.
Isis said to have urged extremists to run over civilians in a poster released over the weekend featuring a knife, handgun and lorry urging radicals to "gain benefit from Ramadan".
The three men, wearing fake suicide bomb vests, were shot dead by eight officers outside a pub after police opened fire with an "unprecedented" hail of 50 bullets, while a bystander was also shot.
Officers say they know the identities of the men who carried out the attack and will release the names "as soon as operationally possible".
Scotland Yard said seven women and five men aged between 19 and 60 were arrested under the Terrorism Act in Barking on Sunday. A 55-year-old man was later released without charge.
A vigil will be held on Monday evening near London Bridge in honour of the victims of the attack, which took place at around 10pm, while a minute's silence will take place at 11am on Tuesday.
Network Rail said London Bridge rail and London Underground stations reopened at 5am but the rail station will be exit only.
People from around the world were caught up as hundreds cowered in pubs and restaurants, barricading themselves inside as the attackers stalked the streets.
Tales of heroism emerged in the aftermath, with one British Transport Police officer taking on the trio armed only with his baton before being stabbed in the head, face and leg.
An off-duty Metropolitan Police officer was also injured after he tackled the men.
Forty-eight people were left in hospital, 21 critically injured.
As counter-terrorism police units and security services launched a huge investigation for the third time in a matter of weeks, officers arrested a dozen people in raids on flats in Barking, east London, where residents said they believed one of the terrorists may have lived.
One neighbour said one of the attackers had recently asked him how he could hire a van.
