Police are hunting for two men after gas was released on a Tube train in central London on Saturday.
A number of people were treated at the scene at Oxford Circus by paramedics for coughing and lack of breath.
British Transport Police there were no further concerns for their health and their symptoms “would suggest the gas is CS gas”.
Officers hunting for the perpetrators have released CCTV images of two young white men they want to trace after the incident, which was reported at 9.13am.
Anyone who witnessed the incident, or who knows the identity of the men, is asked to contact BTP by texting 61016 or by calling 0800 40 50 40 quoting reference 171 of 20/07/19.