London’s mayor appealed for vigilance and calm Thursday after a stabbing spree in the heart of the city that left one woman dead and five injured.

Police arrested a 19-year-old suspect and said that early indications suggested that “mental health was a factor in this horrific attack.”

However, in the context of a string of recent attacks in Europe, authorities said they were keeping an open mind and that “terrorism remains one line of inquiry being explored.”

London police’s counter-terror chief Mark Rowley said there would be “an increased presence on the streets” of the capital on Thursday, including armed officers — an unusual sight in Britain.

Police arrested the teenager after reports of a stabbing spree in Russell Square, a quiet area close to several popular tourist attractions including the British Museum.

Paramedics fought to save the life of a woman believed to be in her 60s but pronounced her dead at the scene. Two women and three men were also injured but no details have been released about their condition.

The suspect himself was taken to hospital after being immobilised with a Taser electroshock gun.

Xavery Richert, 22, a French tourist staying in a youth hostel on the square, told AFP: “I was buying a beer when I heard a woman shouting who was being chased by a man.

“I thought it was a bag snatching … she was not hurt. I came out for a cigarette, I went back, there were firefighters, police, and then I saw the body under a sheet. You could only see the feet sticking out.”

Russell Square resident Constantine Somerville said: “It’s such a safe area and very quiet especially at night — why would somebody commit an attack in such a quiet area?”

Credit: Guardian