PSNI chief constable Simon Byrne has been criticised for posing alongside officers armed with machine guns outside a police station in Crossmaglen.
His Christmas Day tweet pictured him beside the fortified barracks in south Co Armagh.
Sinn Féin Assembly member Conor Murphy demanded “immediate answers”.
He said: “This post by the chief constable is offensive to the local community and utterly unacceptable.
“It has only served to further undermine the public confidence in the PSNI within South Armagh.
“The heavily armed officers posing with the chief constable is reflective of the militaristic style of policing that the community in South Armagh has had to endure in recent years.”
In recent times Mr Byrne has warned of the opportunities a hard Irish border might provide for dissident republicans.
He visited the border police station and acknowledged the unique nature of policing in the area.
Mr Murphy said: “We need a new chapter for policing in South Armagh.
“We need an end to fortress police stations, heavily armed officers and poor response levels.
“We need a police service that serves the interests of this community in an efficient, effective and respectful manner.
“This community not only deserves nothing less, but will accept nothing less.”
Mr Byrne applauded colleagues who police such a unique part of Northern Ireland.
He said: “Their sense of duty and optimism is inspiring. Stay safe and thank you.”
A PSNI statement said: “The chief constable is happy to meet with any community or political representative who has a positive contribution to make about local policing matters.”
“Unique Part of Northern Ireland”. Commissioner Drew Harris, what do you have say about co-worker in the past, Chief Constable Simon Byrne? It is time to reflect surely. Do people recall what was once common place especially in the area of renown called Crossmaglen. Imagine a return to signposts like these. I have to say I prefer to see Beware of Deer. First I would recommend you look at the photos and then read piece about An Taoiseach Mr Leo Varadkar’s sentiments about a Border Poll. https://www.thejournal.ie/united-ireland-varadkar-4946098-Dec2019/