A 40-year-old man was sexually assaulted next to a busy main road in Caerphilly, police said.
Officers from Gwent Police are investigating the incident which is said to have occurred in a lane off the town's Pontygwindy Road last week.
A statement from a force spokesperson said that the assault took place at approximately 9.55pm on Thursday August 26.
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It added: "The victim was a man in his 40s who is being supported by specialist officers.
"Enquiries are ongoing."
Anyone with information relating to this incident is asked to call 101 quoting 2100301369 or to call Crimestoppers anonymously on 0800 555 111.
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