LONDON —Police in London were searching for the assailant who detonated a homemade bomb Friday that sent a scorching blast of smoke and flame through a London subway car, injuring at least 22 rush-hour commuters and sending panicked crowds scrambling for safety in what police called a terrorist incident.
As of Friday evening, there was no immediate claim of responsibility, and authorities gave no details on possible suspects. But security measures were tightened across London’s vast mass transit network and the government described the threat level as severe.
British media reported the crude device, carried in a bucket and shoved into a shopping bag, had a timer, suggesting that some degree of bomb-making knowledge was employed.
“This was a device intended to cause significant harm,” said Prime Minister Theresa May, but it remained unclear whether the explosive detonated prematurely or malfunctioned at the Parsons Green station, about three miles southwest of central London.
It was not certain if the suspected bomber was among those hurt or on now the run. But in a sign that a manhunt could be mobilized, London police appealed to public to submit their cellphone images taken at the scene.
May called a special meeting of the anti-terrorism Cobra committee late Friday after London police declared the subway explosion a “terrorist incident” on the inbound train, nine stops from Westminster.
Three hours after the incident, President Trump tweeted: “Another attack in London by a loser terrorist. These are sick and demented people who were in the sights of Scotland Yard. Must be proactive!”
It was unclear whether Trump had been briefed by his security advisers, who told him something of the identity of the assailants. Neither the Metropolitan Police nor the British government have said anything publicly beyond describing the detonation as a suspected terrorist attack.
Following Trump’s tweets, and without mentioning the American president by name, May said it’s not “helpful for anybody to speculate on … an ongoing investigation.”
Later, during a brief appearance outside the White House, Trump further hammered a hard-line message, saying “we have to be very smart and we have to be very, very tough — perhaps we’re not nearly tough enough.”
During a tumultuous election campaign which was interrupted by two terrorist attacks, the British Prime Minister repeatedly promised harsh new measures.
May vowed, “if human rights laws get in the way” of protecting Britain, she would change those laws.
At the time, experts wondered whether May’s tough talk could be matched by action, and how a country already considered one of the world’s most proactive on counterterrorism could further turn the screw.
“Even before the attacks this year, British agencies already relied on expansive counterterrorism legislation,” said Raffaello Pantucci, director for International Security Studies at the Royal United Services Institute in London.
“But the threat is now so diffuse that it is unclear how those measures could be more effectively used to prevent future attacks. One of the few possibilities would be to impose harsher sentences for terror-related offenses, and that is certainly something being considered.”
“There are only so many things you can do, though. I don’t think Britons would want to have armed police officers on every street corner,” said Pantucci.
Shortly after the explosion, the right-wing populist United Kingdom Independence Party, UKIP, tweeted: “Thank goodness nobody serious hurt at #ParsonsGreen but we cannot rely on jihadist incompetence.”
“We have hundreds of detectives involved looking at CCTV, forensic work and speaking to witnesses,” said Mark Rowley, head of London’s police counterterrorism unit. “This investigation will be supported by our colleagues at MI5 bringing their intelligence expertise to the case.”
A photograph on social media showed the improvised explosive device — a white bucket beside a shoulder bag sitting on the subway car floor, on fire but showing little damage. Even the bucket was not burned.
Authorities said the 22 injured largely suffered from flash burns. Emergency services said none of the injured faced life-threatening conditions.
Parsons Green is in trendy Fulham, a neighborhood of Victorian rowhouses and leafy parks, known for its furniture designers and Championship League soccer.
Witnesses described a fireball and smoke racing through the subway car, and then a frantic crush of people trying to flee while others attempted to aid those with burns and other injuries.
Luke Walmsley, 33, a film editor, was on his way to work during a normal morning commute, listening to music. And then it was suddenly not normal.
“I heard a scream and then there was a flash, a light, and smoke. I actually pulled my earplugs out, and then the screams got louder and louder,” he said, recalling people running toward him at the station.
“It was chaos. It was every man for himself to get down the stairs, and it’s a very tight exit,” he said, describing injured people on the ground. “I went back to see if they were okay. Other people attended them, then there were nannies and moms asking where their children were.”
He said that on the platform, there were people helping others “who were shocked and burned, bottles of water being poured over burns, quite severe burns, whole legs.”
In the months since May’s narrow re-election, her government has come up with few new proposals. Cities have invested in erecting barriers or bollards to make it harder for terrorists to attack popular public spaces.
Earlier this week, Metropolitan Police in London deployed for the first time new high-tech nets laced with tungsten-steel spurs that can be placed on roadways and stop marauding vehicles as heavy as a London double-decker bus.
“The terrorist threat now includes unsophisticated attacks, such as stabbings and vehicle ramming, where the planning cycle is much shorter than it would otherwise be. This volatility means that the authorities have to intervene a lot earlier,” explained Rajan Basra, a researcher with the International Centre for the Study of Radicalisation at King’s College in London.
Friday’s explosion was the fifth terrorist attack in Britain this year. At least three of the attackers who struck Britain this year were previously known to law enforcement officials. Authorities have acknowledged that it is impossible keep track of all suspects, and it is believed that British security services are constantly monitoring about 500 people. According to E.U. officials, the number of Islamist extremists in the country could be up to 50 times higher.
Experts have warned, however, that the increased frequency of arrests could end up alienating Muslim communities. In France, where authorities have long favored mass arrests and large-scale crackdowns over prevention work and targeted detentions, relations between authorities and Muslim communities have deteriorated in recent years. Security agencies often rely on tips from Muslim communities to prevent plots.
London Mayor Sadiq Khan condemned “the hideous individuals who attempt to use terror to harm us and destroy our way of life. As London has proven again and again, we will never be intimidated or defeated by terrorism.”
Lauren Hubbard, 24, had just stepped on the Tube at Parsons Green — the beginning of her morning commute to her job in the financial district — when she felt intense heat. Then she saw flames barreling toward her.
“I got on, heard a bang, looked around, and this wall of fire is just coming at me. It took up the whole circumference of the carriage.” She said the train was a new one that didn’t have smaller, separate cars, so the flame was just ripping right through it.
“I could see the fire; I could feel the heat of it. At first you just panic, then you just run. There can be no good reason why this is happening, even if this is just an accident like an explosion or Tube fault, there is no reason why a fire like that would or should be on a Tube, so you instantly assume the worst.”
Kate Llewellyn-Jones, 42, who lives next to the Underground station, said she heard shouting and then a woman ran into her yard. She had lost her shoes in the stampede. Llewellyn-Jones took the woman into her home.
This thought struck many: Why attack here? Parsons Green is not a tourist magnet, but a leafy enclave with many cafes, pubs and shops.
“It feels very far away from the center,” said Llewellyn-Jones.
Stuart Lees, a priest who was comforting some of the commuters outside the station, tried to make sense of terrorism flaring in this normally quiet corner of greater London.
“It’s most unusual, to be honest, in this setting,” he said.
On social media, several users living near the Parsons Green station tweeted their support to those affected, responding in a typical British fashion with, “I’ll put the kettle on.”
“If anyone needs a coffee, tea, a quiet moment or just a chat, please DM me — Going home now I am on Dawes Road, 2 minutes to #ParsonsGreen,” Twitter user Maeva Gonzalez wrote.
Police and ambulance arrived at the station in three minutes.
After the recent spate of attacks in London and Manchester, the British prime minister was criticized by the opposition for slashing of local police staffs — and those arguments were raised again after the subway blast.
On Thursday, Britain’s Home Office announced that police, using broader authorities, had arrested a record 379 people for terror-related offenses in the last months, an increase of almost 70 percent.
Jennifer Hassan in London, Paul Schemm in Addis Ababa and Brian Murphy in Washington contributed to this report.