Nine people were treated for life-threatening injuries after a series of stabbings on a train near Cambridge in eastern England on Saturday, and two men were arrested in what Prime Minister Keir Starmer called an “appalling incident.”

British Transport Police said counterterrorism police were supporting its investigation whilst it works to establish the full circumstances and motivation for the incident.

“We’re conducting urgent enquiries to establish what has happened, and it could take some time before we are in a position to confirm anything further," British Transport Police Chief Superintendent Chris Casey said. "At this early stage it would not be appropriate to speculate on the causes of the incident."

Cambridgeshire police said they were called at 1939 GMT after reports that multiple people had been stabbed on the 1825 service from Doncaster in northern England to London King's Cross.

The train stopped at Huntingdon, with armed officers seen entering the train in videos on social media.

"Armed officers attended and the train was stopped at Huntingdon, where two men were arrested," the police said.

One eyewitness told Sky News that one of the suspects, waving a large knife, was tasered by police.

The East of England Ambulance Service said it mobilised a large-scale response to Huntingdon Railway Station, which included numerous ambulances and critical care teams, including three air ambulances.

Starmer posted on X that the incident was "deeply concerning."

"My thoughts are with all those affected, and my thanks go to the emergency services for their response," he said.