Sinn Féin's Martin McGuinness has called on the British government to commit to holding a border poll on the reunification of Ireland in the event of a Brexit.
The Deputy First Minster, who is urging the public to vote on June 23rd to remain in the European Union, described Brexit as a "political and economic game-changer" and said he believed "Ireland's place North and South is in Europe and leading change in Europe".
Secretary of State for Northern Ireland Theresa Villiers is among a number of Tory ministers, including London mayor Boris Johnson, campaigning for the UK to vote to leave the EU.
Provision for a border poll was written into the 1998 Good Friday Agreement and Mr McGuinness said the British government should give a firm commitment to honouring this in the event of Brexit.
Mr McGuinness said: “If Britain votes to leave the European Union then that could have huge implications for the entire island of Ireland and, given all the predictions, would run counter to the democratic wishes of the Irish people.
“If there is a vote in Britain to leave the EU there is a democratic imperative to provide Irish citizens with the right to vote in a border poll to end partition and retain a role in the EU.
“I have proposed to Theresa Villiers that, given the enormous significance of these issues, the British government now give a firm commitment to an immediate border poll in the event Britain votes to leave the European Union.”
However, Ulster Unionist Party (UUP) leader Mike Nesbitt said Ms Villers "would have no basis to call it".
“If you look at the schedules to the 1998 act which makes provision for a border poll the Secretary of State would need to believe there is a realistic prospect that people will vote for change. There is no such evidence base,” Mr Nesbitt said.
The Democratic Unionist Party, led by First Minister Arlene Foster, is campaigning for a vote to leave, as is Traditional Unionist Voice and Ukip.
Sinn Féin, the SDLP, the Alliance Party and the Green Party are backing the remain campaign, as is the UUP, the only unionist party in the North to do so.