Damage to poppy wreaths at Narrow Water in County Down is being treated as a hate crime, police have said.
Eighteen soldiers were killed in two IRA bomb attacks at the site near Warrenpoint in August 1979.
It is understood the damage happened on Saturday at about 17:20 BST. The wreaths have since been replaced.
Cliftonville Football Club said it was “aware of allegations of involvement from persons returning from our fixture in Warrenpoint”.
In a statement, club chairman Gerard Lawlor condemned the incident.
“We live in a sad society where anyone would get a kick out of desecrating a memorial,” he said.
“If anyone connected with our club has any information about the incident then they should report it to the PSNI.
“This pathetic act isn’t in my name nor that of Cliftonville Football Club.”
Cliftonville FC said it understood those involved were not in an affiliated supporters group or supporters club and added that the club would provide “its full cooperation in the investigation of this matter”.
Ch Insp Gerry McGrath said police stopped a bus in Lisburn at about 18:00 and spoke to a number of passengers. The vehicle was then retained by the PSNI as part of the investigation.
Newry, Mourne and Down independent councillor Jarlath Tinnelly said he witnessed the incident on Saturday as he drove past on the other side of the road.
He said a crowd of men gathered at the front of a parked bus, and “three or four” of them were “ripping at the poppy wreaths”.
“The anniversary of Narrow Water was only a couple of weeks ago, so that stuff would have been fresh and new and replaced as it is every year,” he added.
“There were boys just ripping them off and kicking them around as if they were playing about with them in the school yard – it was absolutely incredible to see.
“The most shocking thing of the whole lot was the brazenness of it.”
Mr Tinnelly said he had no hesitation reporting the incident to the police which he described as a “hate crime”.
DUP leader Arlene Foster described the incident as a “twisted act of hatred”.
She added: “Those responsible need to be held accountable for their actions. Desecrating a memorial runs against the natural instincts of humanity.”
Sinn Féin South Down MLA Sinéad Ennis said there was “no place” for such attacks.
“Monuments and memorials are important places in communities and should be respected,” she said.
Ulster Unionist Party (UUP) councillor David Taylor described it as a “deplorable” attack.
“They have vandalised poppy wreaths and destroyed messages left in memory of those who were murdered at Narrow Water,” he added.
TUV leader Jim Allister said: “It will be a test of the community from which the culprits come as to what level of cooperation is afforded in identifying them to the police.”
Police are appealing for witnesses and those who have dashcam or helmet footage who were travelling in the area at about 17:15 on Saturday.
Wreaths at the Narrow Water site were damaged previously in November 2017 and June 2018.
The 1979 attacks at Narrow Water were carried out hours after the Queen’s cousin, Lord Louis Mountbatten, was killed in an IRA bomb attack on his boat in County Sligo in the Republic of Ireland.