Islamic State on Saturday claimed responsibility for the stabbing attack in central London that left two people dead before the attacker was shot and killed by armed police. The Islamist militia's mouthpiece news agency, Amaq, said the man was an Islamic State fighter and that he carried out the attack in response to calls for targeting citizens of the countries that form an alliance fighting Islamic State. On Friday, a man identified by British authorities as 28-year-old Usman Khan stabbed two people to death on London Bridge before he was shot dead by police. The suspect had previously been convicted of terrorism offences, according to British authorities. Three other victims, a man and two women, are receiving treatment in hospital, police said. Accompanied by Home Secretary Priti Patel, British Prime Minister Boris Johnson surveyed the scene late Saturday morning with Metropolitan Police Commissioner Cressida Dick and City of London Police Commissioner Ian Dyson, the Press Association (PA) reported. Khan, who reportedly served time for a plot to bomb the London Stock Exchange, had been released early from prison in December 2018, prompting a fierce debate about the practice. The Times newspaper said that he was still wearing an electronic ankle tag. London Bridge attacker was former terror convict, British police say The Guardian reported that the judge in Khan's case said his plans were a “serious, long-term venture in terrorism” and he may represent an ongoing danger to the public. "[It is a] mistake to allow serious and violent criminals to come out of prison early and it is very important that we get out of that habit and that we enforce the appropriate sentences for dangerous criminals, especially for terrorists,” Johnson said before chairing a Friday evening meeting of the British government's emergency committee Cobra. Responding to criticism, the Parole Board issued a statement on Saturday to say it had not been involved in his release of the attacker “who appears to have been released automatically on licence (as required by law), without ever being referred to the Board.” Queen Elizabeth sent her “thoughts, prayers and deepest sympathies to all those who have lost loved ones” and praised the “brave individuals who put their own lives at risk to selflessly help and protect others.” Khan's attack started at a conference on rehabilitation at Fishmongers' Hall; he was tackled by ex-offenders attending it and a Polish chef who worked at the venue, PA reported. Khan, who was wearing a hoax explosive device at the time of the attack, had taken part in a prisoner rehabilitation programme organised by Cambridge University and had shown “no cause for concern,” PA cited a source familiar with the programme as saying. Campaign events for the upcoming British general election on December 12 were cancelled on Saturday. Commissioner Dick confirmed to journalists that the attacker is believed to have acted alone, PA reported.