Transport police are seeking a man in connection with an attack at a South Yorkshire train station.
Police have released CCTV images of a man they are seeking in connection with a serious assault at Swinton station in Mexborough.
The "unprovoked attack" left a man with a broken jaw which required surgery.
The victim was travelling on board a Northern rail service travelling between Leeds and Sheffield at 10:20pm on Saturday April 14 when the attack happened.
A spokesman for British Transport Police said: "The victim was on the train when he went to use the onboard toilet facilities. Whilst waiting in a queue, he spoke with three other men.
"As the journey continued, the men became aggressive, punching the victim to head. The victim fell to the ground and was then kicked multiple times by the three men.
"The attackers are thought to have left the service at either Moorthorpe, Thurnscoe, Goldthorpe or Bolton-on-Dearne station."
Officers would like to speak with the man in the CCTV images, as they believe he may have information which could help with the investigation.
Anyone who recognises him or has any information which could help, should text British Transport Police on 61016 or call 0800 40 50 40 quoting ref 149 of April 15.