LONDON -- A homemade bomb planted in a rush-hour subway car exploded in London on Friday, injuring 29 people and prompting authorities to raise Britain's terrorism threat level to "critical," meaning another attack may be imminent.
The early-morning blast sparked a manhunt for the perpetrators of what police said was the fourth terrorist attack in the British capital this year.
Prime Minister Theresa May, acting on the recommendation of the Joint Terrorism Analysis Center, raised the country's threat level from "severe" to "critical" -- its highest possible level. May said soldiers would augment the police presence in a "proportionate and sensible step."
Earlier, May said the device had been "intended to cause significant harm."
Experts said the bomb -- hidden in a plastic bucket inside a supermarket freezer bag -- only partially exploded, sparing the city much worse carnage.
"I would say this was a failed high-explosive device," Chris Hunter, a former British army bomb expert, said of the blast, which caused no serious injuries.
The Islamic State terrorist group claimed responsibility for the explosion on its Amaq news website. Experts cautioned that the group often takes credit for attacks it may have inspired, as well as ones it had nothing to do with.
It was not certain whether the bomber was among those hurt or was now on the run. In a sign that a manhunt could be mobilized, London police appealed to the public to submit cellphone images taken at the scene. British media said investigators had closed-circuit television images of a suspect. The homemade device blew up on the inbound train, nine stops from Westminster.
The bomb went off about 8:20 a.m. as the train, carrying commuters from the suburbs -- including many schoolchildren -- was at Parsons Green station in the southwest of the city.
Witness Chris Wildish told Sky News that he saw "out of the corner of my eye, a massive flash of flames that went up the side of the train," followed by "an acrid chemical smell."
Lauren Hubbard, 24, had just stepped on the Tube -- as London's underground train service is known -- at Parsons Green when she felt intense heat. Then she saw flames barreling toward her.
"I could see the fire," she said. "I could feel the heat of it. At first you just panic, then you just run. "
Chaos ensued as hundreds of people, some of them suffering burns, poured from the train, which can hold up to 800 people.
"I ended up squashed on the staircase. People were falling over, people fainting, crying. There were little kids clinging onto the back of me," said another commuter, Ryan Barnett.
Passenger Luke Walmsley said it was "like every man for himself to get down the stairs."
"People were just pushing," he added. "There were nannies or mums asking where their children were."
Kate Llewellyn-Jones, 42, who lives next to the station, said she heard shouting and then a woman ran into her yard. She had lost her shoes in the stampede.
This thought struck many: Why attack here? Parsons Green is not a tourist magnet but a leafy enclave.
"It feels very far away from the center," Llewellyn-Jones said.
Police and health officials said 29 people were treated in London hospitals, most of them for flash burns. None of the injuries were serious or life-threatening, the emergency services said.
Trains were suspended along a stretch of the London Underground's District Line, and several homes were evacuated as police set up a 150-foot cordon around the scene while they secured the device and launched a search for those who planted it.
The Metropolitan Police said hundreds of detectives, along with agents of the domestic spy agency MI5, were looking at surveillance camera footage, carrying out forensic work and speaking to witnesses.
Speaking to reporters late Friday, Assistant Commissioner Mark Rowley said police were making "good progress" and that the public should be reassured that more police and troops will be on the streets.
"We are only aware of one device," he said. "We have remnants of that device. We are chasing down suspects." He refused to provide further details, except to say the bomb involved the "detonation of an improvised explosive device."
Among the questions authorities were seeking to answer: What was the device made from, and was it meant to go off when it did, in an affluent part of the city far from London's top tourist sites?
British media reported that the bomb included a timer. Lewis Herrington, a terrorism expert at Loughborough University, said that would set it apart from suicide attacks like those on the London subway in 2005 or at Manchester Arena in May, in which the attackers "all wanted to die."
Photos taken inside the train showed a white plastic bucket inside a foil-lined shopping bag, with flames and what appeared to be wires emerging from the top.
Terrorism analyst Magnus Ranstorp of the Swedish Defense University said that from the photos it appeared the bomb did not fully detonate, as much of the device and its casing remained intact.
"They were really lucky with this one; it could have really become much worse," he said.
Hunter, the explosives expert, said it appeared that "there was a bang, a bit of a flash, and that would suggest that, potentially, some of the explosive detonated, the detonator detonated, but much of the explosive was effectively inert."
Police and ambulances were on the scene within minutes of the blast. The city has been a target for decades: from Irish Republican Army bombers, right-wing extremists and, more recently, attackers inspired by al-Qaida or the Islamic State group.
Britain has seen four other terrorist attacks this year, which killed a total of 36 people. The other attacks in London -- near Parliament, on London Bridge and near a mosque in Finsbury Park in north London -- used vehicles and knives. Similar methods have been used in attacks across Europe, including in Nice, France; Stockholm; Berlin and Barcelona, Spain.
The last time the country's threat level was raised to critical, was after the May 22 suicide bombing at Manchester Arena that killed 22 people.
British authorities say they have foiled 19 plots since the middle of 2013, six of them since the van and knife attack on Westminster Bridge and Parliament in March, which killed five people. Police and MI5 say that at any given time they are running about 500 counterterrorism investigations involving 3,000 individuals.
London Mayor Sadiq Khan said there had been a "shift" in the terrorism threat, with attackers using a wide range of methods to try to inflict carnage. Khan, who belongs to the opposition Labor Party, said London police needed more resources to fight the threat. Police budgets have been cut since 2010 by Britain's Conservative government.
TRUMP WEIGHS IN
President Donald Trump's suggestion that London police could have done more to prevent Friday's bomb explosion drew a quick rejoinder from May, who said it's never helpful "to speculate on what is an ongoing investigation."
Trump turned the explosion into an opportunity to highlight his tough talk on terror and promote his travel ban.
The president's series of early-morning tweets about the still-unfolding investigation stood in contrast to his delay last month in firmly condemning neo-Nazis and white supremacists after racial violence broke out in Charlottesville, Va., and left one person dead. At the time, he said: "When I make a statement, I like to be correct. I want the facts. ... I don't want to rush into a statement."
On Twitter, Trump called the explosion another attack "by a loser terrorist." He also offered implied criticism of law enforcement, saying "these are sick and demented people who were in the sights of Scotland Yard. Must be proactive!"
Asked about Trump's comments, May said, "I never think it's helpful for anybody to speculate on what is an ongoing investigation."
Trump told reporters Friday morning that he had been briefed on the explosion, but did not provide further details.
Trump's national security adviser, H.R. McMaster, suggested later that the president was speaking generally. Noting that law enforcement has been working to combat terrorism for years, McMaster said, "If there was a terrorist attack here, God forbid that we would say that they were in the sights of the FBI."
"I think he means generally that this kind of activity is what we are trying to prevent," McMaster said.
The White House said Trump and May spoke Friday. White House spokesman Sarah Huckabee Sanders said Trump's tweet "may have come up" but gave no further detail.
Trump also used the moment to argue on Twitter that his travel ban targeting six mostly Muslim nations should be "far larger, tougher and more specific - but stupidly, that would not be politically correct!"
And Trump promoted his handling of extremist militants, saying the government should cut off Internet access for such groups.
"Loser terrorists must be dealt with in a much tougher manner. The internet is their main recruitment tool which we must cut off & use better!" he wrote on Twitter. He argued that his administration has "made more progress in the last nine months against ISIS than the Obama Administration has made in 8 years."
Trump concluded, "Must be proactive & nasty!"
Information for this article was contributed by Jill Lawless, Gregory Katz, Lori Hinnant and Catherine Lucey of The Associated Press; and by William Booth, Karla Adam, Rick Noack, Paul Schemm, Brian Murphy and Jennifer Hassan of The Washington Post.
A Section on 09/16/2017