The British government has said Gerry Adams’ claims Brexit will destroy the Good Friday Agreement are unfounded.
The Sinn Fein president alleged fundamental human rights enshrined in the 1998 accord to end violence could be undermined.
The top legal adviser to Stormont ministers has said not one word in the Agreement would be affected.
A statement from the Government said none of the institutions and provisions set out in the Belfast Agreement, including those relating to human rights, are in any way undermined by the decision of the UK to leave the EU.
It added: “These comments are totally without any basis in fact.”
The Sinn Fein leader said Northern Ireland should enjoy special status within the union of 27 states after Brexit, and claimed that would not affect the constitutional settlement which secures its status as part of the UK.
The Government said: “The UK Government is fully behind the implementation of the Belfast Agreement and its successors, including Stormont House and Fresh Start. There will be no return to the borders of the past.
“We are also working intensively to ensure that following the forthcoming election strong and stable devolved government that works for everyone is re-established in Northern Ireland.”
Mr Adams, a Dail TD (member of the Irish parliament), addressed a conference on achieving a united Ireland in Dublin on Saturday.
He said: “The British Government’s intention to take the North out of the EU, despite the wish of the people there to remain, is a hostile action.
“Not just because of the implications of a hard border on this island, but also because of its negative impact on the Good Friday Agreement.
“The British Prime Minister repeated her intention to bring an end to the jurisdiction of the European Court.
“Along with her commitment to remove Britain from the European Convention on Human Rights, this stand threatens to undermine the fundamental human rights elements of the Good Friday Agreement.”