Mr Gerry Adams has warned that the Belfast Agreement could be in danger of "crashing" because of unionist insistence on making a "big issue" of the decommissioning of arms.
The Sinn Fein president, in his first major speech since last week's referendum, said: "It is frankly worrying that since the document was signed, there are already signs that the British Government is buckling under unionist pressure to depart from what was agreed at Stormont. This appears to be taking place in regard to what is called decommissioning."
While promising that Sinn Fein will try to work the agreement, Mr Adams warned: "The unionist attitude of recalcitrance and intransigence, of resentment and minimalism, may still manifest itself in an obstructive and wrecking mode."
He continued: "The sad history is there of a sort of `Twilight of the Gods' mentality whereby they would prefer to bring down the whole show with them rather than share power and justice with their nationalist fellow citizens."
He denounced the view of consent and self-determination in the agreement as one "no Irish republican could accept" because "it rests on the gerrymander of Partition."
But he said there was nothing in the document "which can be construed as binding one to the Document's flawed definition of self-determination.
"We held, and hold, that Ireland is the valid constituency for mapping out the future of the people of the island, and without eternal interference. However, it is not feasible to proceed in that way immediately, not least because of the attitude of the British government.
"So we must see how we can advance the position without a negation of principle," he said. "No other party has been asked to abandon its philosophy and analysis. Nor will we abandon ours, and there is nothing in the document which compels us to do so."
Addressing the American-Irish Historical Society in New York at the start of his five-day US fundraising visit, Mr Adams said that the "immediate task" should be to convince people and "armed groups" that weapons are no longer required.
He set out a detailed list of demands for nationalists in the areas of civil rights, justice and policing and economic development.
"The RUC is unacceptable" and "unionist militias can be no part of a settlement.
"All repressive laws have to be repealed; the judiciary fundamentally reformed; demilitarisation of British military installations has to begin and conclude quickly; British troops should go; licensed firearms should be recalled, and all political prisoners have to be released."
He also called for the setting up of a Department of Equality.
The North/South ministerial council must not be "frustrated by unionist obstruction or undermined by British vacillation," but should be "developed and expanded."
Mr Adams called on the British government "to state a positive position, on behalf of the British people, on the issue of Irish unity and its desirability." He would like the Irish Government and the US administration to "encourage such a step."
Referring to Good Friday as evoking for some "an image of crucifixion", Mr Adams said, "There are those who will maintain that is what happened to Irish republicanism on April 10th this year." But he was one of those for whom "the cause of a united Irish republic was in fact given new hope and fresh possibility" by the agreement.
Later Mr Adams attended a Sinn Fein fund-raising dinner at the Plaza Hotel on Central Park.
Today he will meet the editorial boards of the New York Times and Newsday. Later he will visit the floor of the New York Stock Exchange and a fund-raising
event in the International Trade Centre.
Tomorrow he will give a press conference in Washington and visit the White House to meet officials. It is possible that he will also meet President Clinton.