A woman was killed and several people were injured in a mass stabbing attack in central London late Wednesday, police said.
The attack occurred in London's Russell Square near the British Museum, London Metropolitan Police said in a statement.
A suspect was arrested after police discharged a Taser at him. He was identified as 19-year-old man. He was under guard in hospital.
The suspect's mental health "appears to be a significant factor" in the stabbing incident, but a terrorist background could not be ruled out, a police spokesman said.
No additional details on the suspect's identity were disclosed.
The woman was treated at the scene but pronounced dead soon after. She was believed to be around 60 years old.
Two women and three men sustained "various injuries."
"Terrorism is one possibility being explored at this stage," the police statement said.
The killing is being investigated by the London Metropolitan Police's Counter Terrorism Command.
Additional police units were deployed to the area.
On Wednesday London police had announced that it would deploy armed police in London due to the threat of terrorist attacks. British police are generally not armed.