Two people have been arrested in connection with a murder in Woolwich today.
Metropolitan Police commissioner Sir Bernard Hogan-Howe said:
It is hard to comprehend the shocking and horrific scenes we have seen this afternoon on a busy street as Londoners went about their day as normal.
We have launched a murder investigation, being led by the Counter Terrorism Command. Two men have been arrested in connection with that murder.
We understand concern about the motivation and we will work tirelessly to uncover why this occurred and who was responsible. I understand people want answers, but I must stress we are in the early stages of investigations.
I would urge everyone to remain calm and have a measured response to today's tragic events.
In Greenwich we have met with community representatives, and extra officers remain on duty there tonight.
Across London our officers are in contact with their communities too. The shock that we all feel at what has happened must bind us together.
ITV News has uncovered a video showing Woolwich suspect Michael Adebolajo speaking at a demonstration at Harrow Central Mosque in 2009.
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Police in Kenya say they did everything they could to highlight their concerns about Michael Adebolajo.