The London Underground station where an improvised device exploded on a train reopened early Saturday as a huge manhunt for those responsible for the terrorist attack entered its second day.
The device went off while the train was stopped at Parsons Green station in southwest London during the Friday morning rush hour, injuring at least 29 people. The incident prompted UK authorities to raise the national threat level from "severe" to "critical," meaning an attack is expected imminently.
Less than 24 hours later, the suburban Tube station was back in use by travelers, although with a visible police presence outside as it first opened its doors. An officer on the scene told CNN that transport through Parsons Green was "back to normal."
The train which was attacked Friday could no longer be seen on the track, which is above ground at this point.
Meanwhile, hundreds of police officers are scouring CCTV footage, questioning dozens of witnesses and studying the remnants of the device in search of clues to the identity of those responsible for placing the device on the train.
No arrests have yet been announced.
Prime Minister Theresa May announced late Friday that the UK terror threat level had been raised to its highest level.
"The public will see more armed police on the transport network and on our streets, providing extra protection. This is a proportionate and sensible step which will provide extra reassurance and protection while the investigation progresses," May said. "The threat of terrorism that we face is severe but together, by working together, we will defeat them."
The Prime Minister said people should carry on with their daily lives, but be vigilant.
Police: 'Excellent progress'
Mark Rowley, assistant commissioner of the London Metropolitan Police, said late Friday that investigators were making "excellent progress" toward identifying, locating and arresting those behind what police have labeled a terrorist attack.
Detectives have spoken to 45 witnesses and received more than 70 images and video clips from the public, he said.
Britain's armed forces have also been called in to support the police as they work to keep the public safe.
"Military personnel have been drafted in to protect national infrastructure sites, allowing additional armed police officers to carry out patrols," a Met Police statement said, adding that people can expect to see more police, some of them armed, "at crowded places, iconic sites, transport hubs and ports" this weekend.
Mayor Sadiq Khan told Londoners they should "rest assured the full resources of our police and security services are being deployed to track down those responsible. They will be caught and brought to justice."
He also thanked the police and London's transport body, Transport for London, in a tweet Saturday for their "hard work to keep our city moving."
The British Transport Police tweeted: "Nationwide, extra officers from BTP are on duty today. If you see something suspicious, don't delay."
ISIS claimed involvement with the explosion, saying via its Amaq news agency that a "detachment" from the group had carried out the attack. When asked about possible ISIS involvement, Rowley told reporters that it is "routine" for the extremist group to take responsibility for attacks in "these sorts of circumstances," regardless of its actual involvement.
ISIS provided no evidence to back up its claim.
'Everyone started running'
Scenes of panic broke out Friday at Parsons Green as the explosion went off in a busy train carriage.
"Suddenly, there was this boom," eyewitness Gustavo Vieira told CNN. "Everyone shouting and screaming... We were just leaving the carriage [when the explosion happened]... everyone starting running... and I didn't look back."
At least 29 people were injured in the incident, most of them with flash burns, according to Rowley. None are thought to be in a serious or life-threatening condition, the London Ambulance Service said.
A photograph taken by a witness showed what looked like a large plastic bucket in a supermarket carrier bag with wires trailing from it and flames licking the top.
A British security source who was briefed on the investigation told CNN that a timer was found on the device. It's clear the device was intended to cause much greater damage, the source said, but cautioned that the investigation is still in its preliminary stages.
Another source briefed by investigators told CNN that an initial assessment of the device indicates it is "highly likely" to have contained the explosive TATP but that this has not been confirmed. It also appeared to have been crude and poorly designed, the source said.
Trump: 'We have to be tougher'
US President Donald Trump told reporters in the White House Rose Garden on Friday that "we have to be tougher and we have to be smarter" in dealing with the terrorist threat.
Later, speaking to members of the United States Air Force at Joint Base Andrews near Washington, Trump said "radical Islamic terrorism" would be eradicated.
His comments followed controversy over tweets he posted earlier in the day in which he railed against "loser terrorists" and suggested that the perpetrator was known to UK authorities and recruited on the Internet.
Those tweets prompted May and a London police spokesperson to publicly rebuke the President.