BRITAIN is on critical terror alert with military troops set to bolster police forces as police hunt for the Parsons Green tube bomber.
A manhunt is under way after the improvised explosive device (IED) sent a fireball through a packed London Underground train carriage in south west London, during yesterday's morning rush-hour.
A total of 29 patients needed hospital treatment, with a number of those hurt suffering from burns.
Police were called at around 8.20am following reports of a fire on the District line train as it pulled in to the station.
Emergency services including armed police went to the scene and cordoned off the station.
Witnesses described scenes of terror and panic as the blast sent a "fireball" and a "wall of flame" through the carriage at Parsons Green station.
Images emerged on social media appearing to show wires protruding from a flaming bucket inside a plastic Lidl carrier bag on the floor of a carriage, while reports suggested the device had a timer.
Sylvain Pennec, a software developer from Southfields, near Wimbledon, was about 10 metres from the source of the explosion when fire filled the carriage.
"I heard a boom and when I looked there were flames all around," he said.
"People started to run but we were lucky to be stopping at Parsons Green as the door started to open."
He described the scene of panic as commuters struggled to escape the carriage, "collapsing and pushing" each other.
Mr Pennec stayed behind to take a closer look at what he believed was the source of the explosion.
"It looked like a bucket of mayonnaise," he said.
Chris Wildish, who was on the train, said he saw a "device" in the last carriage.
He told BBC 5 live: "Flames were still coming out of it when I saw it and had a lot of wires hanging out of it – I can only assume it was done on purpose."
Police suspect the explosion was sparked when the device was detonated, and launched a counter-terrorism probe alongside MI5.
The device was being forensically examined last night while police were scouring CCTV and examining witness statements for potential leads.
Prime Minister Theresa May raised the threat level to the highest possible rating, meaning another attack is expected imminently.
Mrs May condemned the "cowardly attack", saying it involved a device "clearly intended to cause significant harm".
She announced military personnel would replace police officers "on guard duties at certain protected sites which are not accessible to the public".
The Islamic-State (IS) terror group claimed responsibility for the attack through its Amaq news agency, according to the US-based Site Intelligence.
Rita Katz, the director of Site, said IS claimed the bombing was the work of a "detachment" rather than simply a "soldier", which she said implied it was a coordinated attack.
But experts have warned their claims should be treated with caution.
Britain has suffered four attacks already this year.
London Mayor Sadiq Khan told LBC radio "there is a manhunt under way as we speak", while Scotland Yard said detectives are making "fast-time" inquiries to establish who was responsible, adding that there have been no arrests.
"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."
As Britain faced up to another terrorist incident, following four attacks already this year:
:: The Prime Minister said the terror threat level would remain at severe - meaning an attack is highly likely - but would be kept under review;
:: Images emerged on social media appearing to show wires protruding from a flaming bucket inside a plastic carrier bag on the floor of a carriage;
:: Reports suggested the device had a timer;
:: A total of 22 patients were being treated in hospital, with a number of those hurt suffering from burns;
:: Scotland Yard and the PM rebuked US President Donald Trump over his claim the Parsons Green Tube bomber was "in the sights" of Scotland Yard.
Assistant Commissioner Mark Rowley, the country's most senior counter-terrorism officer, said "many urgent inquiries" are ongoing.
He said: "We now assess this was a detonation of an improvised explosive device."
Asked if it was clear whether the person responsible was on the train at the time, Mr Rowley said: "It's very much a live investigation and we are following down the lines of inquiry as I said."
Mr Rowley said Londoners can expect to see an "enhanced police presence" and called on anyone with information to contact authorities as a matter of urgency.
The blast comes with the UK on high alert following four terrorist attacks so far this year.
Authorities have foiled 19 plots since the middle of 2013 - including six since the Westminster atrocity in March.
The incident comes a day after figures showed terror-related arrests in Britain have hit a new record high, with suspects held at a rate of more than one every day.
Police and MI5 are running 500 investigations involving 3,000 individuals at any one time, while there are also 20,000 former "subjects of interest" whose risk must be kept under review.
