This comes as counterterrorism officials questioned a friend of Michael Adebolajo, one of two men suspected in the savage killing.
The friend, Abu Nusaybah, was arrested after giving a BBC Television interview Friday about how Adebolajo came to be radicalized.
British soldier Lee Rigby was hacked to death in London Wednesday in the middle of a busy street in the southeast London district of Woolwich. The horrific scene was recorded on witnesses' cellphones, and a video has emerged showing one of the two suspects making political statements and warning of more violence as the soldier lay on the ground.
Adebolajo and the second suspect, 22-year-old Michael Adebowale, remain hospitalized after being shot by police, who arrived minutes after Rigby's slaying.
The attack has sparked fears of anti-Muslim sentiments in Britain. Police on Saturday arrested three people on suspicion of posting racist comments on Twitter, while Faith Matters, a charity campaigning against extremism, said its helpline has received 162 calls since Rigby was killed from people reporting anti-Muslim incidents including attacks against mosques.
Many questions remain over what could have led to the attack on Rigby, a 25-year-old ceremonial military drummer and machine-gunner who had served in Afghanistan and was off duty when he was walking near his barracks. Nusaybah's BBC interview offered one possible narrative. He said Adebolajo's behavior changed after he allegedly suffered abuse at the hands of Kenyan security forces.
Nusaybah said Adebolajo became withdrawn after he was allegedly arrested and then abused both physically and sexually while in jail. He claimed that agents from Britain's domestic spy agency, MI5, approached Adebolajo after he returned to Britain and initially asked him if he had met specific Muslim militants, then asked Adebolajo if he was willing to act as an informer.
"He was explicit in that he refused to work for them," Nusaybah said.
The BBC said police arrested Nusaybah outside its studios Friday night immediately after recording the interview.
It was not immediately possible to verify the information provided by Nusaybah, who said he had known Adebolajo for about a decade. MI5 does not publicly discuss its efforts to recruit informers. It is not uncommon, however, for special services officers to occasionally visit communities to ask people if they know potential terror suspects or others under MI5 surveillance.
The Associated Press contributed to this report.