LONDON (AP) — British police said 10 people have been hospitalized, nine with life-threatening injuries, following a mass stabbing attack on a London-bound train Saturday evening, and that counter-terrorism police are supporting the investigation.

In a statement early Sunday, British Transport Police, which took the lead in the response given that it is responsible for security matters on trains, said two individuals have been arrested in connection with the stabbings.

“Ten people have been taken to hospital with nine believed to have suffered life-threatening injuries,” the statement said. “This has been declared a major incident and Counter Terrorism Policing are supporting our investigation whilst we work to establish the full circumstances and motivation for this incident.”

The police force also said that “Plato,” the national code word used by police and emergency services when responding to what could be a “marauding terror attack,” was initiated. That declaration was later rescinded but no motive for the attack was disclosed.

“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,” Chief Superintendent Chris Casey said. “At this early stage it would not be appropriate to speculate on the causes of the incident.”

The attack took place as the Doncaster to London King’s Cross train headed south toward Huntingdon, a market town a few miles northwest of the university city of Cambridge.

Emergency services, including armed police and air ambulances, responded quickly as the train drew into Huntingdon. The attack appears to have been contained swiftly after the train arrived at the station, and police officers wearing forensic suits, with a police dog, could be seen on the platform.

Cambridgeshire Constabulary, the local police force, said armed police attended the incident after officers were called to the scene at Huntingdon station at 7:39 p.m. on Saturday. It added that the two people were arrested at the station, which is around 75 miles (120 kilometers) north of London.

British Prime Minister Keir Starmer said his “thoughts are with all those affected” after the “appalling incident.”

Paul Bristow, the mayor of Cambridgeshire and Peterborough, said he had heard of “horrendous scenes” on the train.

London North Eastern Railway, or LNER, which operates the East Coast Mainline services in the U.K., confirmed the incident had happened on one of its trains and urged passengers not to travel because of “major disruption.”