One of the suspects in the Woolwich murder was arrested in Kenya in 2010, the UK Foreign Office has confirmed.
It said Michael Adebolajo was arrested there and it gave consular assistance "as normal" in the circumstances.
Boniface Mwaniki, head of Kenya's anti-terrorism unit, told the Associated Press Mr Adebolajo was believed to have been preparing to train and fight with Somali militant group al-Shabaab.
He said Mr Adebolajo was arrested with five others and later deported.
The Kenyan government had previously denied he had ever visited the country.
Mr Adebolajo, 28, and a second man, Michael Adebowale, 22, were arrested on suspicion of the murder of soldier Lee Rigby in Woolwich on Wednesday.
They remain in custody in hospital in a stable condition after being shot and wounded by police at the scene after the killing.
'Approached by MI5'
A friend of Mr Adebolajo, Abu Nusaybah, told the BBC's Newsnight on Friday that the Woolwich suspect travelled to Kenya last year "to study".
But instead, he said, Mr Adebolajo told him he had been detained by "Kenyan troops", interrogated in a prison cell and "beaten quite badly".
Abu Nusaybah said he also believed his friend had been subjected to sexual abuse and his personality had changed after the trip.
Upon his return, Abu Nusaybah said Mr Adebolajo was approached by MI5 who asked him to work for them - a request he rejected.
Photographs printed in several UK newspapers on Sunday reportedly show Mr Adebolajo in the dock in a court in Kenya in November 2010 along with a group of other men.