London attack – as it happened: Theresa May raises threat level to critical as Isis claims responsibility

Soldiers to support police after 29 people are hurt in tube bombing at Parsons Green

Parsons Green attack: What we know so far

The UK's terrorist threat level has been raised to critical after London was hit by a new terror attack as commuters headed to work on the Tube.

An explosion at Parsons Green underground station in the west of the capital injured passengers and led to a "major incident" being declared. Yet more people were hurt during the crush to leave the train, witnesses said.

Images shared online appeared to showed a bucket with wires trailing from it smouldering inside a District Line train.

The device is being forensically examined while detectives are scouring CCTV and examining witness statements for potential leads.

Armed police, paramedics and firefighters were all called to the scene.

Witnesses described flames and a "fireball" following the incident at about 8.20am today.

Assistant Commander Mark Rowley, who is the UK's top counter-terrorism officer, said the force continues to "chase down suspects" in connection with the attack.

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Key Points

• Explosion at London Tube station leaves 29 injured
• UK terror threat level increased to 'critical', the highest level
• Met deploys extra 1,000 armed officers to hunt terror suspects on the run
• Isis claim responsibility for attack
• 'That could have been me': Parsons Green residents try to process local bomb attack
• Police dismiss Donald Trump terror suspect claim, saying 'we don't even know who the suspects are'

[15 September 2017 11:18 · Andrew Griffin]

Here's a report from the Press Association's Hayden Smith on how the incident will be investigated:

Details about the Parsons Green blast are still emerging, but Scotland Yard had declared a "terrorist incident" within two hours of the first emergency calls.

Investigators will be scouring CCTV and taking statements from dozens of witnesses as they attempt to piece together the lead-up to the explosion.

Pictures circulating on social media appeared to show wires protruding from a bucket inside a plastic carrier bag, but officers have so far said it is "too early" to confirm the cause of the fire.

If there is a device, it will be forensically assessed after being made safe, while police will be urgently trying to establish whether someone attempted to detonate it, and whether they were present at the scene.

The scenes of panic evoked memories of the July 7 atrocities in 2005, when suicide bombers killed 52 people in a series of co-ordinated attacks across the transport network.

Two weeks later, a group of men attempted to set off rucksack devices but the bombs failed to go off.

The emergency at Parsons Green will spark another huge counter-terrorism probe as security services confront an unprecedented threat.

Four attacks - at Westminster, Manchester, London Bridge and Finsbury Park - have hit Britain already 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 revealed terror-related arrests in Great Britain have hit a new record high, with suspects held at a rate of more than one every day.

Police warned there is no such thing as a "typical terrorist" after official statistics showed rises in numbers detained across ethnicities and age groups.

There were 379 arrests for terrorism-related offences in the year ending June 2017, the highest number in a 12-month period since data collection began in 2001.

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.

[15 September 2017 11:20 · Andrew Griffin]

18 people have been injured and gone to hospital, according to reports. None are thought to be in a serious or life-threatening condition, the London Ambulance Service said.

It's not clear how man of those were hurt by the explosion, and how many by the stampede that followed.

[15 September 2017 11:33 · Andrew Griffin]

Nigel Holness, London Underground's director of network operations, said: "Our staff have worked to assist the emergency services and to ensure the safety of our customers during this morning's incident at Parsons Green.

"We are focussed on assisting the police investigation into what happened and providing support for our customers and staff.

"Our Sarah Hope Line is available to offer help and support to anyone affected by this morning's incident."

[15 September 2017 11:38 · Andrew Griffin]

Jeremy Corbyn has tweeted: "Thoughts with those injured in Parsons Green terrorist incident, and thanks to police, ambulance staff and firefighters who are responding."

[15 September 2017 11:39 · Andrew Griffin]

Scotland Yard confirms that "that this was a detonation of an improvised explosive device".

[15 September 2017 11:40 · Andrew Griffin]

The police asks that anyone with information call them as a matter of urgency.

[15 September 2017 11:43 · Andrew Griffin]

Donald Trump has responded to the attack: "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!"

[15 September 2017 11:52 · Jon Sharman]

Donald 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!"

[15 September 2017 11:55 · Jon Sharman]

Donald Trump continued: "The travel ban into the United States should be far larger, tougher and more specific-but stupidly, that would not be politically correct!"

[15 September 2017 11:59 · Jon Sharman]

The BBC reports the improvised explosive device used at Parsons Green had a timer.