One of the suspects in the brutal murder of a soldier in Britain was arrested in Kenya three years ago and questioned over alleged links to Islamist insurgents, the Keynan government confirmed on Sunday.
Michael Adebolajo was detained in 2010 but was handed over to British intelligence agents and deported because there was insufficient evidence to charge him, authorities said.
"He was arrested under a different name, a fake name," government spokesman Muthui Kariuki told AFP.
"We did not process him, he was handed over to the local MI5."
A Kenyan anti-terrorism police officer said Adebolajo was arrested over links to Shebab insurgents.
The Shebab are an Al-Qaeda-linked group fighting in Somalia, but with ties in neighbouring nations including in Kenya's Indian Ocean coastal region.
The officer, speaking on condition of anonymity, said Adebolajo had been in contact with other suspects that Kenyan police were tracking in the port city of Mombasa.
"There was no evidence to nail him so he was released. He was interrogated both in Mombasa and Nairobi," the officer told AFP.
The Kenyan government rejected allegations made by a friend of Adebolajo that he had been physically assaulted while being held in Kenya.
On a video of his court appearance in Mombasa in 2010, Adebolajo can be heard saying: "These people are mistreating us, we are innocent."
The government spokesman said "senior members of the intelligence community... denied knowledge of the torture ordeal".
Reports in Britain said Adebolajo was detained on the island of Pate, a few kilometres away from Lamu, which is a crossing point to Somalia.
Adebolajo brother-in-law claimed on Sunday that Britain's perceived lack of concern for his well-being while in Kenya had radicalised him.
"He was a lot quieter and quite bitter towards the fact that he wasn't getting any help from anyone," the relative told ITV News.
The disclosure raises fresh questions about the monitoring of Adebolajo and the other suspect in the murder, 22-year-old Michael Adebowale. It has been reported that both were previously known to Britain's intelligence services, but neither were considered a risk to life.
Adebolajo was captured on video carrying bloodied knives and a meat cleaver after Wednesday's attack saying he had killed off-duty soldier Lee Rigby because British troops were killing Muslims.
Anti-terror investigators in France meanwhile were probing whether the stabbing of a soldier in Paris as he patrolled a busy shopping centre and transport hub on Saturday afternoon was a copycat attack.
The soldier suffered a wound to the neck but was said to be in a stable condition in hospital.
President Francois Hollande said no link to the grisly murder in London had been established "at this stage", but the French interior minister said there were similarities.
The distraught family of Lee Rigby visited the scene of his murder near his barracks in Woolwich, southeast London, and added their bouquets to an ever-growing pile of floral tributes at the scene.
The two men accused of hacking him to death remain under armed guard in separate hospitals after they were shot by police at the scene.
Police arrested a 22-year-old man in London on Sunday on suspicion of conspiracy to murder and were still holding three men in their 20s they detained on Saturday on the same charge.
Both the suspects in the murder are Muslim converts from Nigerian Christian families, raising fresh concerns in Britain about the radicalisation of young men.
Home Secretary Theresa May, the interior minister, warned there were "potentially" thousands of people at risk of being radicalised and said that "all the indications" pointed to last week's attack being a lone wolf-style incident.
In Paris, counter-terrorism investigators were studying CCTV footage of the stabbing of 23-year-old soldier Cedric Cordier as he was on duty in the La Defense district.
Interior Minister Manuel Valls said: "There are elements, the sudden violence of the attack, that could lead one to think there could be a comparison with what happened in London."
The soldier's girlfriend, Amelie, on Sunday revealed that he was still in distress and was living in fear that the attacker was going to find him and "finish the job off".