A man was raped in a Greater Manchester park, police have said.
The 36 year old was approached by two unknown men as he sat on a bench in Broadfield Park, Rochdale at about 18.30 GMT on Tuesday.
After a brief verbal exchange, one of the men restrained him while the other raped him, police said.
Officers want to trace a man and woman who shouted at the perpetrators, causing them to run off in the direction of the Broadfield Hotel.
The bench where the assault took place is on a path which runs alongside Sparrow Hill, police said.
The suspects are both described as Asian, of large build, and in their late 20s or early 30s.
One had black hair and a goatee beard and was wearing dark clothing and footwear that was red at the heel and white towards the front.
The other was clean shaven and wearing a grey hoodie with Nike written across the chest, grey jogging pants and white boxer shorts with small, red checks.
Det Insp Damian Simpson said the actions of the two witnesses "are likely to have saved the victim from suffering even further" in this "ruthless attack" and said their "co-operation could be of significant value" to the investigation.