UPDATES WITH PRIME MINISTER'S STATEMENT; EDITS THROUGHOUT
LONDON (AA) - British Prime Minister Theresa May said the U.K.'s terror threat level will remain at its second-highest level following an explosion on a London Underground train on Friday morning.
May spoke following a high-security COBRA meeting of ministers, military, police and intelligence officials. Police are treating Friday's explosion as a terrorist incident.
The Metropolitan Police said emergency services were called to Parsons Green station in west London at 8.20 a.m. local time following reports of a fire on a commuter train.
Britain's National Health Service (NHS) said 22 patients were taken to London hospitals. Earlier, the London Ambulance Service had said 18 people were being treated for non-life-threatening injuries.
"The threat level remains at 'severe'," May said.
"That means that a terrorist attack is highly likely. But this will be kept under review as the investigation progresses. The public should go about their daily lives but remain vigilant. People who are travelling in London will see an increase armed police presence on the transport network and security will be increased," she added.
The U.K.'s five-step threat level goes up to "critical" -- meaning an attack is expected "imminently", according to domestic intelligence agency MI5.
"We do need to ensure that we are dealing with, not just the terrorist threat but with the extremism and the hate that can actually incite that terrorism," May added. "That’s why we are looking very carefully at the powers that our police and security service have to make sure they have the powers they need."
The U.K. leader also said it was not helpful for “anybody to speculate on what is an ongoing investigation”.
Earlier U.S President Donald Trump, who had criticized London Mayor Sadiq Khan following another attack in the British capital in early June, also reacted to the latest incident.
"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!" he wrote on Twitter.
"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!"
Khan earlier on Friday said London “utterly condemns the hideous individuals who attempt to use terror to harm us and destroy our way of life”. He urged Londoners to “remain calm and vigilant”.
- 'IED'
Britain's senior counterterrorism officer Mark Rowley said in a news conference most of Friday's injured had received "flash burns". Rowley said the explosion was caused by a suspected improvised explosive device (IED).
He said more police would be deployed across London, especially on the capital's transport network.
Images from the inside of the passenger train posted online showed a white bucket with wires protruding from it, on fire, inside a supermarket bag.
Parsons Green station and the roads around it were cordoned off and police advised people to avoid the area as a manhunt to find the perpetrator continued.
Footage from the scene also showed passengers being led off a train by police.
The ambulance service said it had sent a special hazardous area response team to the scene, amid reports of a white substance being found.
Britain has been on high alert following four terror attacks in London and Manchester this year which led to 36 deaths.
Around five million people use London's metro system daily.
In 2007, 52 people were killed in underground train and bus explosions in a series of coordinated suicide bomb attacks in London.
-Turkey condemns blast
In a statement on Friday, the Turkish foreign ministry said it was “with deep sorrow” that it had learned of the attack.
“We strongly condemn this terrorist attack targeting innocent people," the statement read, adding: “We will continue to be in solidarity with our ally the United Kingdom in the fight against terrorism.”