Reading stabbings: Police declare the three killings a terror incident
A 25-year-old man from Reading was arrested at the scene of the attack at about 19:00 BST on Saturday, which also left three people seriously injured.
Counter-terrorism police are now taking over the investigation, Thames Valley Police said.
Security sources told the BBC the man arrested is thought to be Libyan.
Speaking on the BBC’s Andrew Marr Show, Mr Hancock said Home Secretary Priti Patel and Prime Minister Boris Johnson would be in contact with police leading the investigation later on Sunday.
“It’s clearly a terrible crime whatever the motivation and we will be making sure the police have all the support they need,” he said.
The prime minister met security officials, police and senior ministers at Downing Street on Sunday at 09:00 BST and was updated on the ongoing investigation.
An eyewitness to the attack at Forbury Gardens, a park near the centre of Reading, said he saw a man moving between groups of people in the park, trying to stab them.
The arrested man had previously been in prison in the UK for a relatively minor conviction, not a terrorism offence, sources told the BBC.
At the scene
By Linda Serck, BBC News
Reading appears desolate and in mourning this morning. Large areas outside the gardens are taped up and there are not many people here, mainly journalists and their TV cameras.
A strong wind is rattling litter in grey, deserted streets, most of which are being patrolled by armed police. Commuters are struggling to get to work as so many roads have been cordoned off with police tape.
The few people arriving from Reading station expressed “shock”. Marie Castro from Slough works at a Costa coffee shop in Reading and said: “I was scared to be here but I have to be here for work.”
The attack “doesn’t seem right for Reading”, she added.
“It’s multicultural and really friendly. I was really shocked when I heard the news”.
A block of flats on Basingstoke Road in Reading was raided by more than a dozen armed police officers carrying shields at about 23:00 BST on Saturday.
About an hour and a half after they entered, a loud bang was heard at the scene, after which several of the armed officers left.
Craig O’Leary, chairman of the Thames Valley Police Federation, said the “swift action” of officers at the scene prevented “potentially more lives from being lost”.
“There are barely words to describe their bravery – officers who ran towards danger with the sole thought of protecting the public we serve,” he said.
