British police and intelligence services are working to unravel a reported plot by ISIS terrorists to detonate a pressure-cooker bomb at V-J Day commemoration ceremonies in London this weekend.

Sky News reported early Tuesday that it had learned of the plot from a woman named Sally Jones, a British convert to Islam who is fighting alongside ISIS in Syria. Sky said that Jones communicated with undercover reporters who used fake online profiles to give the impression that they were interested in joining ISIS.

Jones told the undercover reporters that she had previously given instruction to three British nationals who were potential terrorists, but who had so far failed to attack. The undercover reporters were told that ISIS policy is for would-be jihadists to remain in their home country and not travel to Syria to join the terror group.

Sky said that it had informed the anti-terror branch of London's Metropolitan Police about the plot against the V-J Day commemorations, which will be attended by Queen Elizabeth II, British Prime Minister David Cameron, World War II veterans, current service members and other dignitaries. In addition, thousands of spectators are expected to crowd the streets for a parade of veterans and current troops from Horse Guards Parade to Westminster Abbey. 

Over the weekend, the Mail on Sunday reported that authorities had undertaken an urgent review of security preparations for the ceremonies commemorating the surrender of Japan to the allies in World War II, which will last several hours and take place at three locations in the heart of the British capital.

Investigators believe the plot involves the detonation of a pressure cooker bomb like those used in the Boston Marathon bombing on April 15, 2013. On that day, twin bombs placed near the finish line of the legendary road race killed three people and injured more than 260 others.

Late Sunday, the Metropolitan Police issued a statement encouraging people to attend Saturday's ceremonies in response to the Mail on Sunday's report.

"While the UK threat level from international terrorism remains severe, we would like to reassure the public that we constantly review security plans for public events, taking into account specific intelligence and the wider threat," the statement said. "Our priority is the safety and security for all those attending or involved. The public are encouraged to continue with their plans to attend or take part in events as normal."

The Mail on Sunday reported that no arrests had been made, but counter-terrorism officers were monitoring reports and chatter about the plot. 

Sky News also reported Tuesday that a former member of ISIS' internal security force had claimed that "four or five" English nationals had been trained to carry out terror attacks and had since returned home. The former jihadist said he knew little about what their plans were after they returned to Britain, but said they were trained in a variety of weaponry -- "using the Kalashnikov, the pistol, the bomb, grenades and other things," as he put it.

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