The Islamic State has claimed responsibility for the latest London terror attack through its propaganda wing Amaq News Agency, the SITE intelligence group reported Sunday.

The terror network reportedly claimed a "detachment" of its fighters crashed a rented van into a crowd of people on London Bridge before going on a stabbing rampage Saturday night, killing seven people and wounding nearly 50 others. However, ISIS gave no evidence to back up its claim.

Earlier on Sunday, British Prime Minister Theresa May condemned the “evil ideology” behind the London attacks.

May addressed the attacks Sunday after a meeting of the government’s COBRA emergency committee. She called for a tougher stance against extremists and tougher controls on cyberspace to prevent its use by extremists.

She said the measures were needed because “terrorism breeds terrorism” and attackers copy each other.

Counterterrorism police carried out raids in east London and arrested 12 people in connection with the attacks. "Searches of a number of addresses in Barking are continuing," London Metro Police said as the raids were being conducted.

The homes raided included one belonging to one of the three terrorists who carried out the attacks, Sky News reported.

"He's lived here for about three years," neighbor Damien Pettit said. "He's one of our neighbors. I've said hello in passing more than 50, 60 occasions. He has two young kids. He was a very nice guy."

ISIS has claimed responsibility for a series of attacks in recent years -- but police have pushed back in some instances. The terror network announced it was behind the deadly attack on a casino and shopping complex in the Philippines last Friday -- but Manila police said the killer was a Filipino gambling addict heavily in debt, with no terror links.

Saturday’s horror began around 10 p.m. local time when a white van veered off the road and barreled into pedestrians on London Bridge. The van’s three occupants then jumped out with large knives and attacked people at bars and restaurants in nearby Borough Market, police said.

Elizabeth O’Neill said her son was stabbed in the stomach by a man who approached him and yelled “this is for Islam.”

Daniel O’Neill, 23, suffered a 7-inch knife wound, she said, according to Sky News. He was recovering.

"He had just stepped outside the bar for a second and a man ran up to him and said 'this is for my family, this is for Islam' and stuck a knife straight in him,” the mother said.

Gerard Vowles, 47, told local media that he saw the three attackers stabbing a woman at the south end of London Bridge. He said he threw chairs, glasses and bottles at the attackers in a bid to stop them.

"They went 'this is for Allah' and then they just started stabbing her multiple times,” he told Sky News.

The Guardian quoted Vowles as saying, “They kept coming to try to stab me. They were stabbing everyone. Evil, evil people.”

He added, according to the paper, "I want to know if this girl is still alive. I've been walking around for an hour and a half crying my eyes out. I don't know what to do."

Brad Myers, an American vacationing in London, told “Fox & Friends” Sunday that he had just taken some pictures and was about to walk along the Thames River when he heard a noise.

“Then I saw the van come on to the pavement and continue along the side of the road just right where I was a few moments before, just mowing down pedestrians,” he said.

“Everyone was in shock,” he said.

What he saw reminded him of the truck attack in Nice, France.

“It’s crazy to think I was right there,” Myers said.

Eight police officers killed the attackers after arriving on the scene within eight minutes.

The officers fired 50 shots, London's assistant police commissioner Mark Rowley said at a press briefing Sunday, calling the number unprecedented. One of the bullets struck an innocent bystander. The person was recovering in a hospital.

Rowley said that the officers had no choice.

"The situation these officers were confronted with was critical - a matter of life and death - three armed men, wearing what appeared to be suicide belts, had already attacked and killed members of the public and had to be stopped immediately," he said.

It turned out the suicide belts were fake.

Rowley said the van had been rented recently by one of the attackers.

May said 48 people were injured and many had life-threatening injuries. Thirty-six remained hospitalized Sunday.

A courageous cop was one of the wounded. He confronted the three knife-wielding terrorists armed only with a baton. He was stabbed in the face, head and a leg. He was in stable condition.

British Transport Police Chief Constable Paul Crowther said of the officer that "it became clear that he showed enormous courage in the face of danger."

Crowther added that "for an officer who only joined us less than two years ago, the bravery he showed was outstanding and makes me extremely proud."

Those killed included a Canadian and a French national.

May said the Thursday's national election would be held as scheduled because "violence can never be allowed to disrupt the democratic process." Major parties suspended national campaigning Sunday out of respect for the victims.

Speaking to Fox News from London, Secretary of Homeland Security John Kelly said the latest attacks mark the fourth or fifth time he's had to call his British counterpart in just four months on the job because of "terrible events like this."

It was the third terror attack to hit Britain in as many months.

In March, a British convert to Islam ran down people with a vehicle on Westminster Bridge, killing four, then stabbed a policeman to death outside Parliament.

On May 22, a British suicide bomber killed 22 people and injured dozens at an Ariana Grande concert in Manchester. After that attack, Britain's official threat level from terrorism was raised to "critical," meaning an attack may be imminent. Several days later it was lowered to "severe," meaning an attack is highly likely.

ISIS claimed responsibility for those two attacks.

The Associated Press contributed to this report.