The killing of three people in a stabbing rampage in a park in Reading is being treated as a terrorist attack, police have said.
A 25-year-old Libyan national is being held by police over the incident,in which at least three other people sustained serious injuries.
Thames Valley police said the attack had been declared a terrorist incident and Counter-Terrorism Policing South East would be taking over the investigation.
Multiple sources confirmed the suspect was Khairi Saadallah, a Libyan refugee.
Security sources told the Guardian he had been granted asylum and had previously been in prison in the UK for a relatively minor conviction, not a terrorism offence.
The head of counter terrorism policing, Metropolitan police Assistant Commissioner Neil Basu, said: “From our inquiries so far, officers have found nothing to suggest that there was anyone else involved in this attack and presently we are not looking for anyone else in relation to this incident.”
He added: “Although the motivation for this horrific act is far from certain counter terrorism policing have taken responsibility for leading the investigation.”
Basu said 41 witnesses had so far come forward.
Boris Johnson chaired a meeting at 9am on Sunday morning in No 10 to be updated on the latest developments, Downing Street said.
“The PM was updated on the ongoing investigation into the fatal stabbings in Reading yesterday,” a spokesman for the prime minister said.
The home secretary, Priti Patel was present, as well as police and security officials.
Home Office sources said the suspect was a Libyan national.
Johnson, Patel and the Labour leader, Keir Starmer, were among senior public figures to have expressed condolences to the family and friends of the victims.
DCI Ian Hunter said: “We have made one arrest and at this stage we are not looking for any other people in connection with this incident. There is no intelligence to suggest that there is any further danger to the public. However, we urge people to remain vigilant and report anything suspicious by calling police.”
CT officers were seen among a group of police officers entering a block of flats in Reading understood to have been the suspect’s home.
More than a dozen armed police officers carrying shields were seen entering the block at about 11pm.
The suspect returned to the property a few weeks ago but had been quiet since then, he added.
A neighbour, Mohamed Seliman, 29, said the suspect returned to the flat a a few weeks ago and had been quiet.
There were several witnesses to the attacks, which took place at 7pm in the popular Forbury Gardens, home of the Maiwand Lion statue, the image of which has been adopted by Reading football club and the Reading Post newspaper.
Disturbing videos on social media showed scenes of victims receiving resuscitation treatment.
Lawrence Wort, 20, a personal trainer, said he was about 10 metres from the attack.
“The park was pretty full, a lot of people sat around drinking with friends, when one lone person walked through, suddenly shouted some unintelligible words and went around a large group of around 10, trying to stab them,” he told reporters.
“He stabbed three of them, severely in the neck, and under the arms, and then turned and started running towards me, and we turned and started running.
“When he realised that he couldn’t catch us, he tried to stab another group sat down. He got one person in the back of the neck and then when he realised everyone was starting to run, he ran out the park.”
Claire Gould, a freelance journalist who lives near the scene, told PA Media she saw emergency air ambulance vehicles land on the nearby Kings Meadow as a police helicopter circled overhead.
She described hearing sirens and said surrounding roads and a retail park had been cordoned off by officers.
At least two casualties were being treated in the emergency department of the Royal Berkshire Hospital.
The prime minister earlier tweeted: “My thoughts are with all of those affected by the appalling incident in Reading and my thanks to the emergency services on the scene.”
The home secretary said in a statement: “This evening we saw a senseless attack on people simply enjoying a Saturday evening with family and friends. My heart, prayers and thoughts are with all of those affected and to the people of Reading who will be deeply shocked and concerned by this terrible incident.
“I am in contact with the police and will ensure they have all the support they need. I would like to thank Thames Valley police and the emergency services for their response.”
Thames Valley police said the incident was not linked to a Black Lives Matter protest that took place in Reading earlier in the day.