Police arrested a dozen people Sunday in connection with the terrorist attack on London Bridge and Borough Market that killed seven people and injured nearly 50.

Authorities said the 12 people were arrested in the Barking neighborhood of East London. The BBC reported that those arrested were eight men and four women. Searches were also being carried out at properties in the area, police said.

Prime Minister Theresa May called an emergency meeting of members of her Cabinet to deal with the third terrorist attack in Britain in three months. The attacks have claimed the lives of at least 34 people, including 22 in a suicide bombing at singer Ariana Grande’s concert in Manchester last month.

In Saturday night’s assault, attackers ran a van into pedestrians on London Bridge, and then stabbed victims indiscriminately with large knives in nearby Borough Market, a popular dining spot. Three suspects were shot to death by police within minutes of the rampage’s beginning.

The attack bore a chilling resemblance to an earlier one in March. In that incident, a man plowed his truck onto the sidewalk of London’s Westminster Bridge, killing four bystanders in the shadow of the Houses of Parliament, and then knifed to death a police officer.

May said Sunday that “five credible plots” had been foiled since the March attack.

“We are experiencing a new trend in the threats we face, as terrorism breeds terrorism and perpetrators are inspired to attack not only on the basis of carefully constructed plots after years of planning and training, and not even as lone attackers radicalized online, but by copying one another and often using the crudest of means of attack,” she said, adding: “It is time to say enough is enough.”

Police said that “the investigation into last night’s horrific attack in London is progressing rapidly.” The head of Scotland Yard, Cressida Dick, appealed for calm and vigilance.

“This is a very worrying time for people,” Dick said. “I would ask people in London, Londoners and visitors, to remain calm.”

Organizers of Sunday evening’s One Love concert, in aid of the victims of the May 22 bombing at the Manchester Arena, said the event would go ahead as planned. On Sunday afternoon, concertgoers were already beginning to enter the Emirates Old Trafford Cricket Ground under tight security procedures involving bag searches and sniffer dogs. Tens of thousands of people are expected to attend the show, whose lineup includes Grande, Justin Bieber, and Katy Perry.