LONDON • British police have arrested an 18-year-old man in the southern port of Dover in connection with Friday's London Underground train bombing that injured 30 people.
The teenager, whose identity has not been revealed, is being held under anti-terror legislation.
The arrest is "significant" but the terror threat level remains at "critical", police deputy assistant commissioner Neil Basu said yesterday.
Hours after, armed police searched a house in Sunbury-on- Thames, Surrey, about 120km from Dover, where ferries sail to France.
Prime Minister Theresa May raised Britain's terror threat level late on Friday to "critical", meaning an attack may be imminent. Soldiers and armed police were deployed to secure strategic sites and hunt down perpetrators.
The home-made bomb shot flames through a packed commuter train during the morning rush hour in west London but apparently failed to detonate fully.
ABOUT THE BOMB
HOW WAS THE BOMB PLANTED?
It is believed that the suspect boarded the train carrying the device inside a supermarket bag, the media reported yesterday. The Independent said police were still investigating if the suspect had left the train before it reached Parsons Green station or had fled amid the chaos as the blast sparked a stampede among panicked commuters.
Five stations could have been the entrance point for the suspect, the BBC reported. As the London Underground is covered extensively by CCTV, whoever carried the device would have been captured on scores of cameras , it said.
WHAT WAS THE BOMB COMPOSED OF?
The crude device, believed to have been made with the explosive triacetone triperoxide (TATP) known as Mother of Satan, contained nails in a bucket with Christmas lights hanging off it.
TATP is a highly fragile chemical favoured by militants. But the home-made device in this case may have a faulty timer that failed to ignite the main bomb, The Australian reported, citing experts.
Dozens of people would have been killed and hundreds seriously hurt if the bomb had detonated as planned, police said.
WHAT ARE THE FIVE THREAT LEVELS?
They give a broad indication of the likelihood of a terrorist attack, Britain's security service MI5 said.
• Low means an attack is unlikely.
• Moderate means it is possible.
• Substantial means it is a strong possibility.
• Severe means it is highly likely.
• Critical means it is expected imminently.
"We have made a significant arrest in our investigation this morning," said Mr Basu, who is Senior National Coordinator for Counter Terrorism Policing. The investigation was continuing, he added.
The blast at Parsons Green station, which reopened yesterday morning, was the fifth major terror attack in Britain this year. The Islamic State in Iraq and Syria (ISIS) claimed responsibility.
"This has become the new normal," said Parsons Green resident Harry Walker. "We get attacked, and then we carry on, waiting in anticipation for the next one."
Britain deployed hundreds of soldiers at strategic sites such as nuclear power plants and Ministry of Defence sites yesterday to free up armed police to help in the hunt for those behind the bombing.
The last time Britain was put on "critical" alert was in May, after a man killed 22 people at an Ariana Grande concert in Manchester.
"For this period, military personnel will replace police officers on guard duties at certain protected sites," Mrs May said in a televised statement. "The public will see more armed police on the transport network and on our streets providing extra protection."
The bomb struck at about 8.20am as passengers, including schoolchildren, were travelling to the centre of London. Some suffered burns and others were injured in a stampede to escape from the station. No one was believed to be in a serious condition.
Pictures showed a slightly charred white plastic bucket with wires coming out of the top in a supermarket shopping bag on the floor of a train carriage. Like the bomb detonated in Manchester, the Parsons Green device contained the explosive triacetone triperoxide, or TATP, and nails, local news media said.
US President Donald Trump raised hackles in Britain after he said on Twitter the "loser terrorist" was "in the sights of Scotland Yard", a reference to the headquarters of London's Metropolitan Police Service. The two countries have close intelligence-sharing ties.
Mrs May complained directly to him when Mr Trump called to offer condolences, according to a British government official.
She was more measured in an interview earlier: "I never think it's helpful for anyone to speculate on what's an ongoing investigation."
In an apparent US leak, CBS reported earlier the explosives were similar to those in another attack.
The bomb struck at about 8.20am as passengers, including schoolchildren, were travelling to the centre of London. Some suffered burns and others were injured in a stampede to escape from the station.
Police said on Thursday that terrorism-related arrests had risen 68 per cent over the past year.
Singapore strongly condemned the attack in London that injured many innocent people, the Ministry of Foreign Affairs said in a statement yesterday. It advised Singaporeans in London to keep in touch with their family and friends.
REUTERS, BLOOMBERG, NYTIMES