Image caption The window display includes the message 'Wishing you an Explosive Christmas'

Police in Londonderry have started an investigation after a snowman holding a rocket launcher was painted on the window of a republican support group's office.

The image includes the message: "Wishing you an Explosive Christmas."

It appeared at the office of the Irish Republican Prisoners Welfare Association, a body that supports republican inmates and their families.

A former mayor of Londonderry described it as "threatening and sinister".

The building - Junior McDaid House - is on Chamberlain Street in Derry and also houses the youth organisation Eistigi Doire as well as the dissident republican party Saoradh - named after the Irish word for liberation.

BBC News NI has contacted organisations in Junior McDaid House for comment.

'Violence on agenda'

Democratic Unionist Party councillor Drew Thompson said many people in the city would find the painting offensive.

"It sends out a message to all communities, not just to unionists, that there are those within the city who are intent in causing destruction over the festive period," he said.

Mr Thompson added that Christmas was a time largely associated with ceasefires during Northern Ireland's Troubles.

"The intent here is certainly not in keeping with the season of peace and good will - it suggests that violence remains on the agenda."

Mr Thompson contacted the Police Service of Northern Ireland (PSNI) to ask if the display was legal.

The PSNI's Supt Gordon McCalmont said he recognised "the hurt and offence caused by this window display".

"We are currently investigating and assessing the matter," he told BBC News NI.