Two more people have been arrested in connection with the death of a soldier in Woolwich.
It brings the total arrested to four people, including the two men shot by police.
Scotland Yard said a man and a woman, both 29, were held on Thursday on suspicion of conspiracy to murder and are being questioned at a police station in south London.
The two men who were shot, aged 22 and 28, have been arrested on suspicion of murder and remain in hospital in a stable condition with non life-threatening injuries.
Drummer Lee Rigby, 25, was hacked to death by two attackers in Woolwich, south east London, on Wednesday.
Six residential addresses are being searched as part of the investigation, three in south London, one in east London, one in north London and one in Lincolnshire.
In a statement the force said: "This is a large, complex and fast-moving investigation which continues to develop.
"Many lines of inquiry are being followed by detectives and the investigation is progressing well."
Officers have recovered a number of items from the murder scene and continue to appeal for witnesses to get in touch, and send in footage and photographs of what happened.
A post mortem examination was taking place on Drummer Rigby's body on Thursday afternoon.Suggest a correction