'Fireball flew down carriage,' passengers badly burned

The crude device could have killed dozens but failed to properly detonate and sent a 'wall of fire' through the carriage injuring at least 18 people including a ten-year-old boy.

Terrified passengers were seen covered in blood with scorched hands, legs, faces and hair – others suffered crush injuries during a 'human stampede' as they 'ran for their lives' at Parsons Green station in west London at 8.20am.

Photographs show what experts believe is a 'pretty unsophisticated' bomb in a flaming white bucket inside a Lidl freezer bag with Christmas lights protruding out of the top — a type of fuse encouraged by ISIS in its online manuals and magazines.

Security sources have said the IED had a timer, indicating the bucket bomber left in on the train and fled before it exploded.

Witnesses said there was a loud 'bang', a flash and then a ball of flame engulfed surrounding passengers on the 'packed' District Line train.

Scotland Yard say it was a terror attack but could not confirm claims there is another device and the suspect is on the run - but an officer at the scene told MailOnline: 'We believe there is a second bomb - there is a man with knives on the loose.'

Witness Luke Warsmey said said he saw a woman with no skin on her legs and a ten-year-old boy with a burned body.

He said: 'The explosion was like a large match going off at the end of the carriage. People just started sprinting. It was every man for himself when that happened. The burn victims had severe leg injuries.

'It was a very busy commuter train, young and old, school children going to their schools. I saw was nannies trying to look for kids, because of the rush of people just taking five and six year olds away from them and they were trying to look for them.'

In the aftermath armed police swooped from the SO-15 counter-terrorism unit performed a hard-stop on a bus in nearby Chelsea Bridge Road. The call was linked to the terror attack but nothing suspicious was found on board.

Donald Trump claim on Twitter that 'loser' London Tube bomber was 'in the sights of Scotland Yard'

Trump tweeted: '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!' Trump tweeted: '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!'

Trump added: '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!'

Trump added: '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!'

President Donald Trump has claimed Scotland Yard was aware ahead of time of a person suspected of setting off a crude incendiary device Friday inside a London subway car.

'Another attack in London by a loser terrorist,' Trump tweeted. 'These are sick and demented people who were in the sights of Scotland Yard. Must be proactive!'

The president also linked Friday's attack at the Parsons Green station attack to his controversial travel ban. He said: 'The travel ban into the United States should be far larger, tougher and more specific – but stupidly, that would not be politically correct!'

Completing his tweetstorm, Trump drew attention to his administration's military action against ISIS and said should the US should get more aggressive with terror groups. 'We have made more progress in the last nine months against ISIS than the Obama Administration has made in 8 years. Must be proactive & nasty!' he wrote.

Prime Minister Theresa May is to chair a meeting of the Government's Cobra emergencies committee this afternoon to discuss the terrorist attack - the fifth major British terror attack this year.

Armed Police, paramedics and firefighters were all said to be at the west London station within five minutes of the explosion today.

A 100m cordon was erected around the station and a police helicopter was also overhead.

The Met confirmed it was a terrorist attack around 40 minutes later. Outside New Scotland Yard on Friday morning Assistant Commissioner Mark Rowley said: 'At 8.20 this morning at Parsons Green tube station there was an explosion on a tube train.

'Police have attended, we now assess that this was a detonation of an improvised explosive device.

'In terms of the police response as you would expect our well practiced command structures have come into shape and operation led and coordinated by the Metropolitan Police with our colleagues at British Transport Police and others. The investigation is being led by the Metropolitan Police Counter Terrorism Command and there are many urgent enquiries on going with hundreds of detectives involved. However, British security services say it is mere "speculation",

"We don't even know who the suspects are so it's a bit difficult to say," a Metropolitan Police source told The Independent. "It's just speculation."

The US President used the terror attack in Parsons Green to call for a "far larger, tougher" travel ban in the US.

More than 20 people were injured when the improvised explosive device ignited on a District Line train.