Police have said they are searching for the person behind a terrorist attack on a packed London Tube train during Friday morning rush hour.
A total of 29 people were hurt when an improvised explosive device went off inside the carriage at Parsons Green station in north-west London.
These are the key facts about the attack:
- The terror suspect behind the attack is still at large
Police say they are still hunting for the person or group behind the terrorist attack.
They say that the blast appears to have been caused by an improvised explosive device which was planted on the train.
It is not yet clear whether security forces have identified a potential suspect, and whether the person who left the explosive acted alone.
Assistant Commissioner Mark Rowley, said Scotland Yard was carrying out "many urgent inquiries" to establish who was responsible for the attacks.
So far no one has been arrested.
- At least 29 people are injured
More than two dozen people were treated in hospital, most of whom have suffered "flash burns".
There are unconfirmed reports that children may be among those hurt, though no one is thought to have suffered life-threatening wounds.
The NHS said that 19 people had been taken to hospital by ambulance, and another ten had come in as walking wounded.
Eyewitness Chris Wildish told ITV News that the flame had shot up towards the roof of the carriage, leaving a number of people with head and face injuries.
"There was one lady whose stockings seemed to have melted into her skin," he said.
"Then there were people who had been hurt in the scramble to get off the train."
- The explosive appears not to have detonated fully
Police sources quoted by the Guardian apparently confirmed that the explosive was "viable" but had not gone off fully.
Academics and chemical experts suggested that the initial flash of the detonation caused the "fireball" described by witnesses.
But it did not alight the explosive within the bucket as intended.
Chemistry expert Professor Hans Michels, from Imperial College London, said the explosive appeared similar to the hydrogen peroxide-based device used in the 2005 London terror attack.
- The UK's terror threat level is not being raised
Prime Minister Theresa May said the UK's terror threat would not be raised to the highest "critical" level as it was after the Manchester Arena attack, and remained at "severe".
That suggests that security forces do not think that whoever planted the device is planning another imminent attack.
Mrs May said people should "remain vigilant" adding: "The threat of terrorism we face is severe but together, by working together, we will defeat them."
- Security chiefs say the attack shows they need more resources
There have been calls for more resources to frustrate terror attacks and additional security for the public transport network in the wake of the latest attack.
Security chiefs have repeatedly warned that the threat they are confronting is more broad than ever before, with violent extremists resorting to a variety of tactics to inflict bloodshed.
Will Geddes, founder of private security firm International Corporate Protection, said that more work needed to be done to protect commuters who have been targeted by extremists a number of times in recent years.