A man suffered "serious injuries" when he was hit with a heavy object, believed to be a metal bar, while on the ground in an assault in west Belfast.
The incident happened in Culmore Gardens on Friday evening.
A second man, who intervened in the assault, was also injured.
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A spokesperson for the PSNI said: "Detectives are appealing for information following a report of an assault in west Belfast on Sunday, April 30."
Detective Sergeant McCartan said: "It was reported on Friday, May 5, that around 8pm on Sunday, April 30, two men were walking in the Culmore Gardens area when they were attacked from behind.
"It was reported that one of the men was struck on the head and fell to the ground, where he was further struck with a heavy object, believed to be a metal bar. He sustained a number of serious injuries, requiring hospital treatment.
"When the second man intervened, he was struck on the arm. He sustained an injury which is not believed to be life-threatening at this time."
The Detectiev Sergeant continued: "It is believed that the suspect was accompanied by a number of other males at the time of the assault.
"Our enquiries are at an early stage and we would be keen to speak to anyone who was in the area at the time and saw anything, or who may have dashcam, CCTV or other video footage.
"The number to call is 101, quoting reference 1596 of 5/5/23.
"Alternatively, you can submit a report online using our non-emergency reporting form via http://www.psni.police.uk/makeareport/.
"You can also contact Crimestoppers anonymously on 0800 555 111 or online at http://crimestoppers-uk.org/ "
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