A woman has died after a stabbing incident in central London.
Here is what we know so far:
A man targeted six people with a knife in Russell Square, central London, at around 10.30pm on Wednesday night.
A woman, believed to have been in her 60s, was fatally stabbed and pronounced dead at the scene.
A 19-year-old man has been arrested on suspicion of murder.
Two women and three men suffered "various injuries" in the attack, with two remaining in hospital and the other three discharged.
A Taser was discharged during the arrest of the suspect. He received hospital treatment and was then taken into custody at a police station in south London.
London Mayor Sadiq Khan urged the public to remain "calm and vigilant".
Counter-terrorism officers are supporting the investigation into the incident, while Scotland Yard said early indications suggest mental health "was a factor". In an earlier statement police had said that terrorism was "one line of inquiry being explored".
The attack raises fears of IS targeting people with mental health problems to inspire them to carry out such incidents.
The attack came hours after Scotland Yard announced that more armed officers would be deployed on public patrol around the capital. Security services are on high alert following a spate of terrorist incidents around Europe. The official threat level from international terrorism currently stands at severe - indicating that an attack is highly likely.
Eyewitness Zuhair Awartani saw the attacker arrested and told the BBC: "He was like African... a dark-skinned man... late 20s probably."
Another person at the scene, Fernando, 40, from Brazil, said he was the first to call the ambulance and saw an "older woman" slumped against the railings with a stab wound to her back, an Englishman with an injury to his upper chest, and a younger girl with a wound on her upper arm. He said: "I was just cycling by when I saw that. The Spanish family just stopped me, just asked me 'Call someone, call an ambulance'.There were three people stabbed. The older woman was slumping against the gates, and it was another two people. One of the Spanish family was comforting the older woman."