A suspect remarked that a District line Tube train was going to be blown up as passengers were targeted in a suspected racist hate crime, police said.
Police said a suspect abused passengers on board an eastbound Tube train between West Ham and Upton Park.
British Transport Police said a male was heard making "inappropriate and offensive comments" on the train on the afternoon of September 19.
The force told the Standard a man aimed comments towards the victims about "how the train may be blown up".
Officers are appealing for witnesses to come forward and have issued CCTV images of a man they want to speak to in connection with the suspected hate crime, which happened between 4pm and 4.20pm.
A spokesman said: “Officers investigating a hate crime on board a District line train in London are today releasing this image in connection.
"Between 4pm and 4.20pm on September 19, two men were overheard making inappropriate and offensive comments on board the eastbound service travelling between West Ham and Upton Park.
"Officers believe the man shown in this image may have information which could help them investigate."
A spokesman added: "He [the suspect] started talking about how the train may be blown up.”
Police have not said how many victims were involved.
Racist hate crimes are on the up in the capital. According to City Hall, 17,560 were reported in the year up to June 2017, the latest for which figures are available. There were 9,720 in the year up to June 2014.
Anyone with information is asked to call British Transport Police on 0800 40 50 40, quoting reference 581 of September 19, 2018. Alternatively, call Crimestoppers anonymously on 0800 555 111.
