LONDON -- British Prime Minister Theresa May has vowed that "things need to change" following the car-and-knife rampage in the heart of the British capital late Saturday.

A short while later, police said 12 people had been arrested in Barking, East London, as officers continued to search a number of addresses in the area.

"We cannot and must not pretend that things can continue as they are," she said in a strongly worded statement to reporters outside her official residence in London on Sunday. "There is — to be frank — far too much tolerance of extremism in our country."

Seven people died and nearly 50 were injured when a van barreled into pedestrians on London Bridge, and then three attackers embarked on a stabbing spree at nearby Borough Market. It was the third terrorist attack on British soil within as many months.

The prime minister said Britain was seeing a "new trend" in the threat the country faces. "Terrorism breeds terrorism" she said, adding that recent attacks were connected by the "evil ideology of Islamist extremism."

She addressed the nation after chairing an emergency meeting of her Cabinet. "Enough is enough," she said as she announced a raft of initiatives to tackle the terror threat.

May said police and intelligence services had foiled five "credible" plots since the attack on Parliament that left three dead in March.

Saturday's incident was reported at 10.08 p.m. (5:08 p.m. ET). Within eight minutes, all of the suspects had been fatally shot by officers, according to authorities.

Police said Sunday among those injured in the attack were a British Transport police officer and an off-duty Metropolitan police officer.

Britain needed to defeat "Islamist ideology," May said, describing it as "the greatest challenge of our time."

Britain also needed to reach international agreements to regulate cyberspace which allows the ideology a "safe space it needs to breed."