Police investigating the vicious killing of an off-duty British soldier on a London street in an apparent Islamic extremist attack say they have arrested a 10th suspect.

London police say the 50-year-old man was arrested east of London on Monday on suspicion of conspiring to murder 25-year-old soldier Lee Rigby. Police didn't provide further details about the suspect's identity.

Rigby was walking near his barracks in southeast London's Woolwich area last week when he was run over by a vehicle and repeatedly stabbed with knives and meat cleavers.

Police have already arrested nine others, including two main suspects shot by officers at the scene of the killing who are hospitalized under armed guard.