The Russia 24 news channel repeatedly aired an old photo of a man with a knife and falsely identified him as the suspect in the attack outside the British parliament in Westminster.
In fact, the image is from a 2013 incident when a man with a knife was tasered outside Buckingham Palace.
Russia 24 also put the image on its website in a short story accompanying the video coverage.
In addition to repeating the claim on live television, Russia 24's parent company Vesti also promoted the false article and image on Facebook, where the company's page has over 1,700,000 followers.
Vesti did not immediately respond to emailed requests for comment, and has posted no corrections or retractions.