A 19-year-old man has been detained shortly after the incident took place at Russell Square, the London Metropolitan PolIce said in the early hours of the day.
Rowley told reporters in a televised press conference that the "spontaneous" attack was "triggered" by mental health issues and is being treated as the primary line of inquiry in the investigation. The assistant commissioner said there were no signs of the assailant's radicalization.
A female victim, previously confirmed to be in her 60s, was further identified by Rowley as a US citizen.
Australian, British, Israeli, US citizens were among those injured in the course of the attack, he added.