London police carried out more raids Monday in connection with their investigation into Saturday's attack that killed seven people and wounded more than 50 others.
Authorities said the Counter Terrorism Command detained "a number" of people during searches at locations in the Newham and Barking areas.
The new detentions add to the 12 people police said had been arrested as of late Sunday.
Islamic State claimed responsibility for the attack through its Amaq news agency.
The violence began with a van striking pedestrians on London Bridge. Police say three men armed with knives then got out of the van and went to a nearby market area where they stabbed numerous people.
Authorities said armed officers shot the three attackers dead within eight minutes of the first call to emergency services. They said canisters the attackers wore, making them look like suicide bombers, were fake.
British Home Secretary Amber Rudd said Sunday that police believe the three who were shot dead by police were the only attackers.
Prime Minister Theresa May said Sunday that three terrorist attacks in Britain in the last three months are "bound together by the evil ideology of Islamist extremism."
There is "far too much tolerance for extremism in our country," May said. "We need to be more robust in identifying and stamping out extremism in public service and across society...it's time to say enough is enough."
May said Saturday's attack does not appear to be connected to the a suicide bombing last month that killed 22 people in Manchester or another attack on Westminster Bridge in March.
But she said "terrorism breeds terrorism" and that the perpetrators are "copying one another."
Bahrain, Kuwait, Oman, Qatar and the United Arab Emirates each issued statements condemning the attack and expressing support for Britain.
伦敦警方星期一展开更多与调查星期六恐袭事件有关的突袭行动，那次恐袭事件造成7人丧生，50多人受伤。
有关当局说，在新汉姆和巴金地区一些地点进行搜查时，“反恐指挥中心”拘捕了一些人。
警方表示，星期天晚上为止，已经有12人被捕，这次行动使被拘捕人数进一步增加。
“伊斯兰国”组织通过阿马克资讯社对本次袭击事件承担责任。
袭击事件始于一辆箱型货车在伦敦桥上将行人撞倒，警方表示，三名持刀攻击者随后从车上跳下来，冲向附近的购物场所，刺伤大量民众。
有关当局表示，在接到第一个紧急报警电话后的8分钟之内，3名袭击者就被武装警察击毙。警方说，袭击者身上有罐状物体，让他们看起来像是自杀炸弹杀手，但是那些物体不是炸弹。
英国内政大臣鲁德星期天表示，袭击者就是被警方击毙的3名行凶男子。
英国首相特雷莎·梅星期天说，过去3个月里英国发生的3起恐怖袭击事件都与“伊斯兰极端主义的邪恶意识形态”密不可分。
这位首相说： “在我们国家，对极端主义太过宽容。我们需要更强有力地找出并铲除公共服务领域和全社会的极端主义......现在是说‘够了'的时候了。”
特雷莎·梅说，星期六的袭击事件看来与曼彻斯特造成22人死亡的自杀爆炸事件以及三月份发生的西敏寺大桥袭击事件无关。
但她说，“恐怖主义滋生恐怖主义”，凶手“互相仿效”。
巴林、科威特、阿曼、卡塔尔和阿拉伯联合酋长国都发表声明，谴责此次袭击事件，并表示支持英国。