Detectives are investigating a YouTube clip which apparently shows a woman hurling racial abuse at a man on the Tube.
Warning: Strong language in video
The footage is believed to have been filmed on an eastbound District line service though the time and date of the encounter is unclear.
British Transport Police (BTP) has released images of a woman they would like to speak to in connection with the alleged episode.
The film was uploaded onto the video sharing website on April 11.
Detective Constable Lawrence Murphy said: "We have isolated images of a woman we believe may be able to help us with our investigation into the incident.
"We believe the footage was filmed on an eastbound District line train, which passed through Stepney Green Tube station and Mile End station.
"At this stage, we urge anyone who witnessed this incident, or who recognises the woman, to get in touch and help us build up a full picture of exactly what took place.
"We treat all allegations of racism very seriously and urge anyone with information about this incident to contact us."
Anyone with information should contact British Transport Police on 0800 40 50 40 or Crimestoppers on 0800 555 111.