A man was attacked and left in hospital after challenging a group of men over not wearing a face covering on the Metro.
Police are investigating the incident which happened on board a train between Pelaw and Fellgate and have now released CCTV images of four men they want to trace in connection.
At around 4.15pm on Sunday May 2, the victim is said to have challenged three male passengers about not wearing a face covering.
One of the men tried to remove the victim’s mask and an altercation took place which involved the victim being punched, the British Transport Police said.
The other men and members of the public intervened, before a fourth man allegedly removed his belt and began to strike those involved.
The victim had to attend hospital, suffering a fractured cheekbone and fractured ribs.
A spokesperson for the BTP said: "Officers believe the men in the images may have information which could help their investigation.
"If you recognise them, or have any information, please contact BTP by texting 61016 or calling 0800 40 50 40 quoting reference 331 of 02/05/21.
"Alternatively, you can call Crimestoppers on 0800 555 111."
