Transcript for Police head off suspected terror attack near Parliament in London

overseas, a frightening scene from London. A new terror scare right near parliament. ABC's Linzie Janis from London. Reporter: Armed officers taking down a suspected terrorist in the heart of the British capital, pinning him against a wall just steps from the houses of parliament. Moments earlier, wrestling the man to the ground in the middle of a crosswalk, discovering knives in his backpack. I think there were about five knives there, up to seven maybe. Reporter: Authorities calling the arrest part of an ongoing counterterrorism operation. The suspect, a 27-year-old British citizen, on their radar. This is where police took down the suspect. You can see it's packed with tourists. The prime minister's residence just a few hundred yards that way and over there, the houses of parliament -- security in the area stepped up after last month's attack. Khalid Masood driving his car at pedestrians on Westminster bridge, killing four and injuring dozens, then stabbing a police officer to death. Today's scene a chilling reminder of a new reality. David, police say they're still investigatinging. No immediate known threat to the public.

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