Seven of the 11 people arrested since the Westminster attack have been released with no further action, police have said.
"Two people arrested as part of the investigation into the terrorist attack in Westminster have now been released from police custody".
A 32-year-old woman arrested in Manchester was bailed pending further enquiries until a date in late March.
British police are combing through "massive amounts of computer data", have searched more than 20 sites and have contacted thousands of witnesses in a vast operation to trace how a British man became radicalized and launched a deadly attack on Parliament, a senior official said Friday. Two people are now in a critical condition - one with life-threatening injuries - in hospital.
Metropolitan Police Acting Deputy Commissioner Mark Rowley told journalists late on Wednesday that five people, including the attacker, died as a result of the terror act.
Masood's last conviction was in 2003, also involving a knife attack.
In the meantime, more details are emerging about 52-year-old Khalid Masood, who was fatally shot by police after he stabbed an officer outside Parlaiment.
Islamic Association of Lincoln Chairman Tanweer Ahmed said: "The Islamic Association of Lincoln condemns the attack on innocent people in London".
A 30-year-old man was arrested in the central city of Birmingham on suspicion of preparation of terrorist acts, London's Metropolitan Police said in a statement.
The 52-year-old was born and raised in Kent and was known to police for a range of previous convictions including GBH, possession of offensive weapons and public order offences. We never surrender, and they couldn't have picked a worser city to affect.
Police officers in Trafalgar Square were approached by numerous people who offered their condolences for the death of their colleague, who was stabbed to death outside parliament by a man police named as Khalid Masood.
Asked about his possible conversion to Islam and subsequent radicalization, Rowley said: "Clearly that's the main line of our investigation, is what led him to be radicalized, was it through influences in a community, influences from overseas, or through online propaganda".
The number of armed officers remains at almost double strength in London in the wake of the attack, Rowley said, while extra police officers are also on patrol elsewhere in the UK.
Police raided the room at the Preston Park Hotel in Brighton after the attack, searching for clues about Masood. It also said that there would be extra officers out on patrols over the next few days.
Within hours, Masood drove his rented SUV across the crowded Westminster Bridge, leaving a trail of dead and wounded.
As we reported Thursday, the attack's victims are from a wide cross-section, representing at least 12 nationalities. Britons have been shocked by the fact that the attacker was able to cause such mayhem in the heart of the capital equipped with nothing more sophisticated than a hired vehicle and a knife. He killed Palmer before another officer shot him to death.
"From the face, from the beard - that is 100 percent him, " she said.
IS militants have been responsible for numerous bloody attacks around the globe, but also have claimed events later found to have no clear links to the group.