British authorities on Monday raised the country's terror threat level to its second-highest level, a day after police said a blast in a taxi outside a Liverpool hospital was caused by a homemade bomb.

According to The Associated Press, investigators said they were treating Sunday's explosion — which killed the suspected bombmaker and injured the cab driver — as a terrorist incident, but that the motive was unclear.

Counterterrorism police named the dead man as 32-year-old Emad Al Swealmeen. They did not give further details, though Britain’s Press Association news agency and other media reported that he had not been on the radar of the security services.

The Joint Terrorism Analysis Centre raised the UK threat level from substantial — meaning an attack is likely — to severe, meaning it is highly likely, following the UK's second fatal incident in a month.

The male passenger in a taxi was killed and the driver injured when a blast ripped through the vehicle as it pulled up outside the hospital on Sunday morning.

Three men in their 20s were arrested elsewhere in the city Sunday under the Terrorism Act and a fourth was detained on Monday. All are believed to be “associates” of the dead passenger, police said.

Prime Minister Boris Johnson condemned the “sickening attack” at Liverpool Women's Hospital and told reporters that the British people “will never be cowed by terrorism.”

“We will never give in to those who seek to divide us with senseless acts of violence,” he said, according to AP.

The attack comes weeks after UK lawmaker David Amess was stabbed multiple times during a visit to a church by Ali Harbi Ali, who considered himself affiliated with the Islamic State (ISIS) terrorist organization.

Britain has been hit by a series of terrorist attacks in recent years.

In February of 2020, a man stabbed and wounded three people in south London before being shot dead by police.

Three months earlier, three people were killed in a terrorist attack at London Bridge.

In May of 2017, 22 people were killed when terrorist Salman Abedi detonated a bomb at the end of an Ariana Grande concert at the Manchester Arena.

London Bridge was also the scene of a terrorist attack in June of 2017 in which ISIS-inspired attackers ran down people on the bridge, killing two. They then proceeded to stab several people to death in nearby Borough Market.