A stabbing rampage in the southern English town of Reading, in which three people were killed and three others were seriously wounded, is being treated as terrorism, police said on Sunday.

A 25-year-old man was arrested on suspicion of murder after the stabbings on Saturday evening in a park in Reading, which is about 65 kilometres west of London.

A British security source told Reuters that the man, who remains in police custody, is a Libyan.

“Counter Terrorism Policing can now confirm that the stabbing incident that happened in Reading last night has now been declared a terrorist incident,” Thames Valley Police said in a statement.

British Prime Minister Boris Johnson, who has described the incident as appalling, held a meeting on Sunday with security officials, senior ministers and police to be updated about the investigation, a spokesman for Johnson said.

Initially police and the government had said the incident did not appear to be terrorism and they were keeping an open mind as to the motive. They said they were not looking for any more suspects in relation to the incident.

The stabbings took place on a sunny evening hours after a rally by anti-racism protesters in the park, Forbury Gardens, but appeared to be unrelated to that.

“The Black Lives Matter event had finished some three hours previous and was by all accounts a very well conducted peaceful demonstration and this is not a connected attack with that whatsoever,” Jason Brock, the head of the local council authority, told the BBC.

Current coronavirus restrictions mean venues like pubs are closed, so many people in Britain gather in parks in the evenings to meet friends.

“Incidents of this nature are very rare, though I know that will be of little comfort to those involved and understand the concern that this incident will have caused amongst our local community,” said Chief Constable John Campbell of Thames Valley Police.

A witness said the attack began when a man suddenly veered toward a group of about eight to 10 friends and began stabbing them.

The nature of the attack was reminiscent of a number of recent incidents in Britain that authorities considered to be terrorism.

In February, police shot dead a man who had stabbed two people on a busy street in south London.

Last November, another man who had been jailed for terrorism offences stabbed two people to death on London Bridge before he, too, was shot dead by police.