The attack took place on Thursday 9 February, when police say at 4.02pm a woman boarded a train at Fishguard and sat in the back carriage.
At around 5pm, two men joined the train at Swansea and sat next to her.
After the train left Swansea station, the men started to speak with the female and try to engage her in unwanted conversations.
On a number of occasions, during this time, both men touched the woman inappropriately. Both men left the train at Llanelli at about 5.20pm.
After they left the train, the female passenger was asked by two fellow passengers if she was okay as they had witnessed the incident.
The first man was white, about 5ft 5” tall, brown hair, clean shaven, average build and carrying a backpack. He spoke with a thick Polish accent.
The second man was white, taller than the first man, brown hair, with a short beard and of slender build. He spoke with a thick Polish accent.
It is also believed that one of the men wore baggy green cargo trousers.
Officers are appealing for anyone who may have witnessed what happened or has any information to come forward and assist the investigation.
Anyone with information is asked to contact British Transport Police by calling 0800 40 50 40 or by texting 61016 – with reference 23000015448.
Information can also be given anonymously to the independent charity Crimestoppers on 0800 555 111.
(Lead image: Hywel Williams / Geograph / Creative Commons 2.0)
