Police are investigating a photograph allegedly showing a person dressed as a Hamas terrorist in Londonderry.
The image is circulating widely on social media.
Some have suggested it is linked to Halloween celebrations in the city in recent days.
The PSNI said it is aware of the photograph and is working to establish its authenticity.
Hamas is a proscribed terrorist organisation in the UK.
The PSNI said the incident may constitute a criminal offence under the Terrorism Act.
The photograph appears to be taken in the Guildhall Square area of Derry.
The person is dressed in combat gear, which has a Palestinian flag badge.
A senior officer said he understood “fully the offence this will cause” given events in the Middle East.
Area Commander of Derry City & Strabane Chief Superintendent Nigel Goddard said: “We are aware of an image posted on social media, and we are working to establish if this is genuine and, if so, when this person was pictured.
“No officer who was on duty in the city centre this week observed this person.
“We understand fully the offence this will cause, and how inappropriate this image is given the events in the Middle East right now. This may also constitute a criminal offence under Section 13 of The Terrorism Act.”
Police have appealed for help in identifying the person.
Mr Goddard added: “From the image that we have right now, this will clearly be extremely difficult to identify the person pictured.
“Therefore, we would ask anyone who saw this person, can assist in identifying this person, or who may have captured this person on their mobile phone to call us on 101. We would also ask the person themselves to contact us to clear this matter up.”
DUP MLA Gary Middleton said he was shocked by the image.
The Foyle representative said: “For anyone to make light of Hamas terrorism in such a way is beyond belief.
“For someone to walk around the city centre like this in broad daylight also raises questions about the level of stewarding and police presence in the area at the time.
“Indeed, such is the grotesque nature, it is hard to believe the photograph is authentic. It is important the authenticity of the photograph is determined, and a full investigation carried out if the photo is real.
“To dress in such a way is the glorification and celebration of a terrorist organisation.”
Mr Middleton said there were incidents during the Halloween parade of participants displaying Palestinian flags.
“The Halloween celebrations in the city are supposed to be non-political but some people appear to have gone out of their way to cause controversy,” he added.
“I have raised this with council officers and will be requesting further information as to what action is being taken by the organisers against those involved.”
Former First Minister Arlene Foster has criticised the Hamas costume photograph.
She posted on X, formerly Twitter: “A Halloween festival with kids milling about and someone decides to dress up as a Hamas terrorist. Glorifying and normalising terrorism has consequences – none of them good.”
Jon Burrows, a former PSNI superintendent, said: “It’s an offence under Section 13 (of the) Terrorism Act 2000 to wear clothing that creates a suspicion you support a proscribed organisation – Hamas is proscribed.
“We cannot be a society that tolerates and normalises this behaviour, whatever our politics.”
The October 7 Hamas attacks killed 1,400 people in Israel and saw 229 people taken hostage.
More than 8,300 people in Gaza have been killed since Israel’s retaliatory bombing began, according to the Hamas-run health ministry.
Israeli troops and tanks pushed deeper into northern and central Gaza on Monday, as Tel Aviv expanded its ground offensive after pounding the territory with air strikes.