The Metropolitan Police commissioner Sir Bernard Hogan-Howe said today that there would be more police officers on the streets of London in order to reassure the public.
The move follows a knife attack in Russell Square last night in which one woman was killed and five people were injured.
"My thoughts are with the family of the woman who was murdered and those who were injured. A normal night out in our busy capital has ended in horrific circumstances," said Hogan-Howe.
"Our investigation is moving very quickly and our detectives have been working hard throughout the night. As we have already made clear, mental health remains a substantial focus for our investigation."
The Met commissioner added: "Every day in London, my officers patrol and carry out operations to catch criminals in the knowledge that they face risk and danger. I am proud that last night our specialist firearms officers were on the scene in six minutes and, using only a Taser, detained the subject. That demonstrates our commitment to use force in a professional and proportionate way.
"Their swift response undoubtedly helped to prevent more people from getting injured.
"Across our capital today you will see more police officers, armed and unarmed, to reassure the public after recent events overseas. We will protect our Capital and those who live, work and visit our city.
Earlier today, London mayor Sadiq Khan called on Londoners to remain "calm and vigilant" and urged members of the public to report anything suspicious to the police.