LONDON — The British police on Monday declared a blast in a taxi outside a Liverpool hospital a terrorist act and arrested a fourth person after determining that it had been caused by an “improvised explosive device.”
At the same time, local leaders praised the taxi driver as a hero, saying that he had prevented an even bigger calamity. The mayor of Liverpool, in northwestern England, said that the driver had quickly escaped the burning vehicle and locked the doors, trapping the passenger who was carrying the explosives into the taxi. The passenger was the only person killed in the blast on Sunday.
“It is not clear what the motivation for this incident is,” Russ Jackson, the head of counterterrorism policing for northwestern England, told a news conference on Monday, adding that, nonetheless, the blast was being treated as a terrorist act. “Our inquiries indicate that an improvised explosive device had been manufactured, and our assumption so far is that it was built by the passenger in the taxi.”
While attacks of this kind are rare in Britain, the country has been hit by high-profile suicide attacks in recent years. In 2005, there was a series of suicide attacks across London that killed 52 people, and in 2017, an attack on the Manchester Arena, carried out by an Islamist extremist who had met with members of ISIS, killed 22.
According to the BBC, MI5, a British intelligence service, is involved in the Liverpool investigation.
Mr. Jackson described how the blast had unfolded shortly before 11 a.m., when the taxi driver, identified by local news media as David Perry, picked up a man who asked to be taken to the Liverpool Women’s Hospital. As the taxi approached the drop-off point at the hospital, an explosion went off inside the vehicle and engulfed it in flames. Remarkably, the driver escaped with minor injuries.
An initial investigation determined that the passenger had taken an explosive device into the cab. The passenger’s identity is known to the police but has not yet been released publicly.
Security camera footage taken at the scene shows the moment the taxi pulled up at the hospital entrance, before a blast appears to blow the windows out of the vehicle. White smoke can be seen rising from the car as the driver leaps out of the front seat.
Within seconds, the entire vehicle can be seen engulfed in flames.
Joanne Anderson, the mayor of Liverpool, praised the driver’s actions, saying that he had averted greater damage with his quick action.
“The taxi driver, in his heroic efforts, has managed to divert what could have been an absolutely awful disaster at the hospital,” Ms. Anderson told BBC Radio 4 on Monday morning. “Our thanks go to him,” she added.
Prime Minister Boris Johnson said that the driver had acted with “incredible presence of mind and bravery,” according to The Press Association, a British news agency.
Three men aged 21, 26 and 29, were detained in the Kensington area of Liverpool hours after the blast on Sunday, the police said. Their names were not immediately released. A fourth man, age 20, was arrested on Monday, according to the police.
Under the Terrorism Act in Britain, the men can be held for up to 14 days without being charged.
The investigation will now “seek to understand how the device was built, the motivation for the incident and to understand if anyone else was involved in it,” Mr. Jackson said, adding that this “is a reminder that the threat from terrorism remains significant.”
A mile away from the blast site, thousands of veterans, military staff and local leaders were holding a Remembrance Day ceremony in Liverpool Cathedral at the time of the explosion. It is still unclear whether the incident was linked to the event, a commemoration of Britain’s war dead.
“We cannot at this time draw any connection to this,” Mr. Jackson said. “But it is a line of inquiry that we are pursuing.”