An explosion on an underground train at a station in south-west London on Friday left several commuters injured and caused panic in the area.
Several people are said to have suffered facial burns after a reported blast in a bucket towards the rear of the District Line train. Some commuters reportedly were trampled and suffered crush injuries in the rush to escape. Islamic State of Iraq and Syria (ISIS) later claimed responsibility for the attack.
British police arrested three men in south Wales over last week's bombing of a busy commuter train in west London, meaning five people are now being questioned by detectives over the attack which injured 30 people.
A 25-year-old man was arrested on Tuesday evening in Newport, while two others, aged 48 and 30, were detained at another address in the Welsh town in the early hours of Wednesday, London police said.
"This continues to be a fast-moving investigation. A significant amount of activity has taken place since the attack on Friday," said Commander Dean Haydon, head of London police's Counter Terrorism Command.
"We now have five men in custody and searches are continuing at four addresses. Detectives are carrying out extensive inquiries to determine the full facts behind the attack."
A second man has been arrested by police investigating Friday's bomb attack on a London underground train, police said.
The 21-year-old man was arrested in the west London suburb of Hounslow just before midnight on Saturday, the Metropolitan Police force said in a statement.
He was detained under Britain's Terrorism Act and taken to a south London police station, the force added on Sunday.
British police hunting those behind a bomb which injured 29 people on a London train on Friday said they had arrested an 18-year-old man in a move described as significant.
The man was arrested under the Terrorism Act in the southern port area of Dover.
The Islamic State of Iraq and Syria claimed responsibility for the attack.
"The bombing on a metro in London was carried out by a detachment of the Islamic State" group, it said in a statement published by its Amaq propaganda agency.
The UK's terror threat level was raised to critical, which means an attack is imminent, hours after an explosion on a London underground train injured at least 29 people.
British Prime Minister had earlier said the threat level will remain at severe, which means an attack was highly likely, but that was revised by this evening as security forces continue their hunt for the suspected "bucket bomber".
US President Donald Trump’s remarks that the terrorist incident in London as another attack “by a loser terrorist” prompting British Prime Minister Theresa May to rebuke him by asking not to “speculate”.
“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 said in a series of tweets.
“I never think it's helpful for anybody to speculate on what is an ongoing investigation,” May said.
An improvised explosive device (IED) went off on an underground train during the morning rush hour at a busy station in London, leaving at least 29 people injured.
Scotland Yard said a suspected "bucket bomb" exploded and the incident was being treated as a "terrorist attack".
Sources told Sky News on Friday that the bomb that was used in the Parsons Green attack had a timer attached to it.
18 patients have been taken to the hospital after witnesses reported a blast on a commuter train in west London, the city's ambulance service said on Friday, though no one is suspected to have sustained serious injuries.
"We have taken 18 patients to a number of hospitals in London. None are thought to be in a serious or life-threatening condition," London Ambulance said in a tweet.
London Mayor Sadiq Khan said Londoners will see more police on the streets of the British capital after an explosion at a metro station, which officers said was a "terrorist incident."
US President Donald Trump on Friday denounced an attack in London when a blast hit a packed commuter train, and urged authorities and others to take more "proactive" steps, such as better policing of internet use by terrorist groups.
"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!", wrote Trump on Twitter.
British police said a bomb was used during an explosion at a London metro station, which injured 18 people in what officers described as a "terrorist incident."
London's police is being supported by Britain's MI5 intelligence service, he said.
The device used during an incident at a London metro station on Friday did not fully detonate, Sky News reported, citing unnamed sources.
Several people were injured at a London underground station, after witnesses reported a blast on a packed rush-hour commuter train which police were treating as a terrorism incident.
Prime Minister Theresa May will chair a meeting of Britain's emergency response committee later on Friday after an incident at a west London tube station, her office said in a statement.
British authorities are treating this incident at a London metro station as terrorism, the BBC reported, citing unnamed counter-terrorism sources.
The British police, however, said that it was too early to confirm the cause of the fire.
Parts of the Underground services in London have been temporarily suspended following the incident.
British Prime Minister Theresa May’s office said that she is “receiving regular updates”on the incident at the Parsons Green Tube Station in West London.
London firefighters are leading passengers off a train along subway tracks close to station where "incident" occurred, reported AP.
British Counter-Terrorism Police is monitoring the events at the Parsons Green Station, but currently, the British Transport Police is handling the investigation.
Emergency services said they had been called to reports of an incident on a train at Parsons Green station in West London at 8.20 a.m. (0720 GMT), but had no further details of what had happened.
Flames engulfed one carriage and raced along a train on a west London route to Parsons Green, forcing passengers to trample others as they rushed for an exit, an eyewitness told Reuters.
The man said people were trampled on when they fled the train after hearing a whoosh and seeing flames race towards them. He said he did not hear a bang after police rushed to an incident at the station at Parsons Green.
"I just heard a kind of whoosh. I looked up and saw the whole carriage engulfed in flames, making its way towards me," he told Reuters, adding that the train was packed with people.
The London fire brigade has sent six fire engines, two fire rescue units and around 80 firefighters to Parsons Green station after a blast was reported there.
London's ambulance service said it had sent its hazardous area response team to an incident at a west London metro station after reports of a blast.
The British Transport Police is at present on the accident site for relief procedures. The police has advised people to avoid the area around the Parsons Green station.
A woman at London's Parsons Green underground train station told Reuters on Friday she was injured in a stampede.
Eye witnesses told Reuters that people ran for the same door on the tube, leading to people being trampled on after the incident.
Armed police were at the scene, a Reuters photographer said.
A blast on a London underground train left some passengers with facial burns, London's Metro newspaper reported on its website. Police said they were aware of an incident at Parsons Green station in West London and that officers are in attendance. London Ambulance said paramedics were present.
Images posted on Twitter showed a woman being attended to by emergency services sitting on a pavement.
Police said they were aware of reports on social media and would release facts regarding the incident once they could be sure of their accuracy.
Transport for London said on Twitter that there was no service between Earls Court and Wimbledon on the District Line which runs through Parsons Green.
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