Both suspects in the killing of a serving soldier in London were known to security services, senior Whitehall sources have confirmed to the BBC.
One of the suspects is understood to be 28-year-old Muslim convert Michael Adebolajo, according to sources.
He and another man are under arrest in hospital after being shot by police after Wednesday’s attack in Woolwich.
Prime Minister David Cameron has said the UK will “never give in to terror or terrorism”.
Shortly after the killing a man, thought to be Mr Adebolajo, was filmed by a passer-by, saying he carried out the attack because British soldiers killed Muslims every day.