Gerry Adams has claimed Northern Ireland is not bound by the Brexit result.
The Sinn Fein leader said a majority vote in the Province to stay within the European Union must be upheld.
And he told the DUP – their power-sharing partners in the Stormont Assembly who campaigned for a Leave – that they must respect the Remain vote.
Urging the Dublin government to respond to the EU referendum result “on an all-island basis”, he also called for a united Ireland referendum in the time ahead.
“People voted to remain within the EU. That should be upheld,” he said.
Some 56 per cent of the electorate voted Remain in last week’s in/out referendum and 44 per cent backed Leave.
Mr Adams was speaking in the Irish parliament, the Dail, as it was recalled to debate the fall out of the referendum result.
“Some will say we are bound by a so-called United Kingdom vote,” he said.
“Sinn Fein says we are not.
“We need to put the island of Ireland first. We stand by the vote of the people of the north.”
Mr Adams said there is now “a huge responsibility on the Irish government to think nationally – on an all-island basis”.
Stormont ministers should be allowed to deal directly with the EU institutions, he said, through maximum cooperation between the Executive and the Dublin government.
“The Democratic Unionist Party must also respect the Remain vote,” he said.
“The majority of citizens in the north, including many unionists, rejected its exit policy. The DUP should accept this.”
Taoiseach Enda Kenny told the parliament the referendum result set off a “political earthquake”.
Ireland has much more at stake in the aftermath than any other EU country but was ready to work in its own national interests, he declared.
Dublin, Belfast and London would also press to keep the Irish border open.