STORMONT'S four main pro-EU parties have met behind closed doors to discuss last week's Brexit vote.
Sinn Féin's Martin McGuinness is understood to have invited the SDLP, Ulster Unionist and Alliance leaders to explore the potential for forging a united front in response to the Leave camp's shock referendum victory.
The move by the deputy first minister to ally himself with Stormont's fledgling opposition could undermine the recent thaw in relations between the executive's two ruling parties.
The DUP was alone among the north's main parties in campaigning to sever ties with Brussels.
The Brexit vote has sparked deep concern on both sides of the border.
The UK as a whole voted by a four per cent margin to leave the EU, but 56 per cent in Northern Ireland backed remaining.
A source present at Monday evening's meeting told The Irish News: "The discussions were on quite a general level and concerned the very serious implications of Brexit for Northern Ireland.
"We were unanimous in our belief that we needed to protect Northern Ireland's interests and we agreed to come back again."
Writing in The Irish News on Wednesday, Mr McGuinness - who also met DUP leader Arlene Foster on Monday - does not make direct reference to collaborating with the other Stormont leaders but spells out how he wants to see pro-EU parties "working together".
He challenges those who wish to "draw a line under the referendum and move on".
"It is not over – it is a live issue and one in which the implications are now being fully revealed," Mr McGuinness writes.
"It is up to all parties and both governments to fully respect the vote of the people here to remain."
The four parties declined to comment on Tuesday evening on the meeting, which has so far gone unpublicised.
However, commentator Chris Donnelly said the referendum result had pitted the DUP against the other main parties.
"It is likely that Sinn Féin and the SDLP will seek to further bolster the post-Brexit consensus by seeking to develop a shared agenda with the Irish government, all of which could mean that the Fresh Start executive becomes one riven by division and acrimony if common ground cannot be found between Arlene Foster and Martin McGuinness."
The revelation about Monday's meeting comes as Dublin's Minister for Foreign Affairs Charlie Flanagan arrives in Belfast for a series of meetings today, including his first post-referendum talks with pro-Brexit Secretary of State Theresa Villiers.
