The British Transport Police have held a press conference, confirming the two suspects arrested following the Huntingdon train attack were British nationals.
A 32-year-old black British national and a 35-year-old British national of Caribbean descent were arrested on suspicion of attempted murder.
Nine people were initially thought to have suffered injuries after the stabbing in Cambridgeshire, which Sir Keir Starmer described as "deeply concerning".
Four have now been discharged from hospital; however, two patients remain in a life-threatening condition.
The force responded with more than 30 officers within eight minutes of receiving the first emergency call.
There is nothing to suggest the Huntingdon train stabbings were a terrorist incident, British Transport Police Superintendent John Loveless told reporters at the scene in Huntingdon.
He said: "It’s a shocking incident and first and foremost, my thoughts are with the family and friends those who have been affected and those who are injured.
"Approximately 7.42pm yesterday evening, there were calls to the police service in relation to multiple stabbings which took place on board a train service."
The British Transport Police have held a press conference, confirming the identities of the suspects arrested following the Huntingdon train attack
|GB News
He added: "The train departed Doncaster at 6.25pm, and was en route to London King’s Cross Station.
"Officers immediately attended Huntingdon station alongside paramedics, where armed police officers from Cambridgeshire Police boarded the train and arrested two people within eight minutes of the 999 call being made.
"Two men were brought into police custody, where they remain this morning.
"I can tell you that these are: the first male, a 32-year-old male, a black British national and a 35-year-old man, a British national of Caribbean descent, they were both arrested on suspicion of attempted murder.
"As stated, they remain this morning in separate police stations for questioning."
Armed police were deployed to Huntingdon station, where the train had stopped, on Saturday evening after reports that passengers were attacked.
British Transport Police (BTP) revealed that 10 people were taken to hospital after the attack, nine of whom have been left with life-threatening injuries, and declared a major incident.
Counter Terrorism Policing are supporting the investigation.
There have been no fatalities.
Both British men arrested on suspicion of attempted murder remain in police custody, and witnesses described police shooting a man with a taser.
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Cambridgeshire Police said more than 30 officers initially responded to the attack
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The Superintendent added that counter-terrorism police had initially supported the operation, but the incident was now not being treated as terror-related.
He said: "British Transport Police declared a major incident yesterday, and counter-terrorism policing were initially supporting our investigation.
"However, at this stage, there is nothing to suggest that this is a terrorist incident.
"This is a British Transport Police investigation, and we continue to work to establish at pace, the full circumstances and the motivations that have led to this incident.
"At this early stage, it would not be appropriate to speculate on the cause of this incident."
The Prime Minister said: "The appalling incident on a train near Huntingdon is deeply concerning".
"My thoughts are with all those affected and my thanks go to the emergency services for their response.
"Anyone in the area should follow the advice of the police."
The King, in a message released by Buckingham Palace, said: "My wife and I were truly appalled and shocked to hear of the dreadful knife attack that took place on board a train in Cambridgeshire last night.
"Our deepest sympathy and thoughts are with all those affected, and their loved ones.
"We are particularly grateful to the emergency services for their response to this awful incident."
Thameslink said that no trains will call at Huntingdon in both directions until further notice | GETTYNorth West Cambridgeshire MP Sam Carling said: "I'm aware of this awful incident on a train bound for Huntingdon this evening".
"Whilst we don't have the full picture yet - my thoughts are with all of those affected - and a huge thank you to @CambsCops and all other first responders in attendance," he added.
Following the attack, LNER said: "We are aware of an incident involving one of our trains".
"Our immediate concern is for the welfare of our customers and crew who are on board. We are in the process of gathering all the details we can and are liaising with British Transport Police."
Cambridgeshire and Peterborough Mayor Paul Bristow said on X that he heard "reports of horrendous scenes on a train in Huntingdon, Cambridgeshire".
"Thoughts are prayers with everyone affected," he added.
Counter Terrorism Policing are supporting the investigation
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Home Secretary Shabana Mahmood paid tribute to the bravery of staff and passengers, writing on social media: "After last night’s horrific attack, my thoughts today are with the victims, their friends and family.
"My deepest thanks go to the British Transport Police, Cambridgeshire Police, Cambridgeshire Fire and Rescue Service and the East of England Ambulance Service. They responded rapidly, with the utmost professionalism and saved lives.
"I would also like to pay tribute to the exceptional bravery of staff and passengers on the train.
"We now know this attack is not being treated as terrorism, and that two British-born, British nationals have been arrested.
"The investigation is ongoing, and I am receiving regular updates from the police."