Two men suspected of hacking a British soldier to death in a "sickening" attack in Woolwich were already known to security services, it has been confirmed.
One of the men is believed to have been born in Britain, while the other is said to be from Nigeria.
Speaking outside Downing Street, David Cameron said he could not comment directly on reports that the two men were known to the security services.
"The point that the two suspects in this horrific attack were known to the security services has been widely reported, you would not expect me to comment on this when a criminal investigation is ongoing.
"But what I can say is this, as is the normal practice in these sorts of cases the Independent Police Complaints Commission will be able to review the actions of the police and the Intelligence and Security Committee will be able to do the same for the wider agencies.
One of the men has been named in the British media as Lambeth-born Michael Adeboloja, 28.
The Evening Standard reported he had become interested in Islam as a teenager having been raised a Christian.
Radical preacher Anjem Choudary has claimed to have known him, describing him as "a completely normal guy".
The Guardian said Adebolajo was born in Lambeth and is of Nigerian descent. He was a student at Greenwich university, and his family moved to Lincoln in about 2004, the paper said.
The family moved from the area to try to prevent him from getting radicalised, the Standard said.
Sky News said a house raided in Lincoln belonged to Adebolajo's father.
Adebolajo was said to be well-known in the area, for handing out leaflets in Woolwich High Street promoting radical Islamic ideas, Sky reported.
He was reported to have run a stall and criticised the invasion of Iraq and Afghanistan.Suggest a correction