The PUP has called for a police investigation after an Irish Tricolour flag was pictured flying over Stormont - as the DUP demand an explanation from the Northern Ireland Assembly.

The questions were raised after a picture of the Tricolour flag circulated on social media and prompted concerns from the PUP and DUP.

It prompted the PUP to report the incident to the PSNI and the DUP to write to the Northern Ireland Assembly Speaker Mitchell McLaughlin and Chief Executive Trevor Reaney demanding an explanation as to why an Irish Tricolour was erected over Parliament Buildings on Wednesday.

PUP spokesman Winston Irvine took to Twitter with a picture of the flag at Stormont.

He tweeted: "Very serious questions needing to be asked as to how the joker is behind this stunt. P45 is in the post."

He added: "PUP have reported this incident to the police and have urged police to investigate the matter."

It comes one day after the Irish Government joined Northern Ireland parties as the Secretary of State Theresa Villiers convened crisis talks over welfare reform.

DUP North Down MLA and Assembly Chief Whip Peter Weir said he has been "assured by the Assembly that these were rogue actions and are being fully investigated".

Mr Weir said: "Whatever the motivation behind this there must be a full explanation from the Assembly as to who had access to the flag poles and who was responsible for this action. If it was carried out by someone working for an outside contractor then this surely would represent a breach of contract which should result in sanction.

"It would also place an onus on the company to take disciplinary action against those responsible. I have inquired too whether the Union Flags, flying to mark Coronation Day, were interfered with yesterday (Tuesday).

Very serious questions needing to be asked as to who the joker is behind this stunt. #P45 is in the post pic.twitter.com/k3sb4Hb2j3 — Winston Irvine (@propatriaeamore) June 3, 2015

"I have been assured by the Assembly that these were rogue actions and are being fully investigated.”

A police spokesman said: "We are aware of the flag and are investigating the circumstances."

Ulster Unionist MP Tom Elliott condemned the "person or persons" responsible for erecting two republican flags at Parliament Buildings today.

Mr Elliott said: "At lunchtime today two republican flags were briefly flown above Parliament Buildings. They were quickly removed and the Ulster Unionist Party has raised the matter with the Assembly authorities who are investigating.

“I understand that due to on-going construction work on the roof of the building, access is largely restricted to building contractors. There will naturally be a very strong suspicion that the person or persons responsible gained access to the roof because they were working up there.

“What is clear is that whoever was responsible for this incident has let themselves down and perhaps more significantly has let their employers down.

“It was no doubt done to attract attention and cause offence and annoyance. The Ulster Unionist Party will be seeking a full explanation of how this could happen. We are perfectly clear that the Union Flag is the only flag that should fly over Stormont in order to reflect and respect the sovereignty of the United Kingdom.”

A spokesperson for the Northern Ireland assembly said it was investigating the incident.

In a statement it said the roof and fourth floor of Parliament Buildings are currently undergoing construction work and is under the control of "building contractors."

It said: “The Northern Ireland Assembly was made aware that two flags were flown without permission from the roof of Parliament Buildings for a short time today.

The roof and the fourth floor of Parliament Buildings are currently a construction site under the control of building contractors. As soon as the Assembly was made aware of the incident, the flags were removed. The Assembly is investigating the incident.

“The Speaker is clear that the Commission needs to be able to consider this matter in full possession of the facts of the situation. He has invited Commission Members to a briefing tomorrow morning for the Clerk/ Chief Executive to update them on any initial findings surrounding the incident.

"A full meeting of the Commission will then be held on Monday when all Commission Members are available and when it is anticipated that more information will be known."

Belfast Telegraph