The Islamic State (ISIS) claimed responsibility for the stabbing rampage in London that killed two and seriously injured three others. The terrorist organization said through its Amaq news agency that Usman Khan, 28, had acted Friday on its behalf.

"The person who carried out the London attack... was a fighter from the Islamic State, and did so in response to calls to target citizens of coalition countries," ISIS said, referring to a multi-country alliance against the group. No evidence was provided to support the claim. However, the group said the attack was carried out in response to its calls to target countries that have been part of a coalition fighting them.

Metropolitan Police commissioner Dame Cressida Dick said Saturday they believed Khan, a convicted terrorist out on Britain's equivalent of parole, acted alone.

London Bridge
Twitter grab

After visiting the scene and speaking with police, Prime Minister Boris Johnson said people convicted of terrorist offences should not be "out on early release."

"It is clear to me that this guy was out, he had served half of his sentence, he was out on automatic early release, and I have long said that this system simply isn't working. It does not make sense for us as a society to be putting terrorists, people convicted of terrorist offences, of serious violent offences out on early release," he said. "And we argue that people should serve the tariff, serve the term of which they are sentenced. And that's my immediate takeaway from this," he added.

Among those killed was Jack Merritt, 25, a course coordinator with the group that was hosting a prison rehabilitation conference that Khan was attending when he stole two knives and started stabbing people.