People rolling in to work on Thursday morning in London probably noticed an increased presence of anti-terrorism cops on streets and in the tubes; this is because of deadly stabbing in Russell Square, a park near the British Museum and several other tourism attractions.

"As a precautionary measure Londoners will wake up this morning to notice an increased presence on the streets of officers, including armed officers today. We would urge the public to remain calm, alert and vigilant," said Metropolitan Police assistant commissioner Mark Rowley.  "Early indications suggest mental health is a significant factor in this case and that is one major line of inquiry.  But of course at this stage we should keep an open mind regarding motive and consequently terrorism as a motivation remains but one line of inquiry for us to explore," he added during the briefing outside Scotland Yard headquarters.

London Mayor Sadiq Khan also called on the public to remain "calm and vigilant" as police probed the incident.  Mr. Khan said his "heart goes out to the victims of the incident in Russell Square and their loved ones", and that the safety of Londoners his "number one priority".

Police got the call of a man stabbing people in the park at about 10:30 PM local time on Wednesday night.  Officers arrived and used an electric stun gun to subdue the 19-year old suspect, after he killed the victim - reportedly a woman in her 60s - and wounded at least five other people. 

Earlier, UK officials had issued a warning about the inevitability of new terrorist attacks in light of the violent attacks that occurred in France and Germany recently.