Mary Robinson has said that the US' proposed Board of Peace is not a board of peace but it is "the board of the power of one person".
Mrs Robinson is a member of the Elders - a group of global leaders working for human rights.
Speaking on RTÉ’s Morning Ireland, Mrs Robinson said it the Board of Peace is "a delusion of power" by US President Donald Trump.
Mrs Robinson is a former president of Ireland and former UN high commissioner for human rights.
"He's had the power of the United States of America unfettered within the country and outside the country. And we're seeing what that means," she said.
Mrs Robinson said that the United Nations does not need to be replaced, but it does need to be reformed, which the Elders have been calling on for several years.
She said that the charter of the Board of Peace does not include any mention of Gaza, which was the original mandate that was approved by the UN, which she said was "bullied" into agreeing to it being set up.
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"There's no doubt that the members of the Security Council were kind of bullied into agreeing this, the way it can happen. But they didn't agree to this Board of Peace.
"They agreed to a Board of Peace to implement the 20 stage phases of the peace plan of Gaza.
"There's no mention of Gaza, and there's no mention of a mandate from the UN in the Charter.
"So it's nothing to do, this Board of Peace has nothing to do with that. It's a much more general board as I said, of the power of one person".
On Ireland joining the Board of Peace, she said that there is no reason for Ireland to join, saying, "how could any self-respecting country?"
She said there is a "one-man rupture" in the world order. Mr Trump, she said, is "power obsessed", which is very dangerous for the world.
"When President Trump pulled out of the Paris Agreement, and he's now pulled out of the UNFCCC and all the other agencies and international bodies that he pulled out of, no other country is following him.
"And so, the fact that he bullies and uses tariffs and disinvites (Canadian Prime Minister Mark) Carney for that speech and wants to put 100% tariff on Canada, he has become power obsessed now.
"And that is very dangerous for the world, but it doesn't mean that the whole rules-based system is gone.
"It needs stronger, active support, especially from middle and smaller countries who depend on it."
She added: "We need to depend for the future of peace on our planet to make sure the rules-based system survives this power crazy man, which he is."
On events in Minnesota, Mrs Robinson said the Trump administration has used "a barrage of lies" to muddy the facts that are designed to confuse people. But the lies cannot stand up to the videos that show the truth, she said.
She added that she had "certainly seen the elements that were certainly what built up fascism in Germany [in the 1930s].
"The elements are there, there's no doubt about it."
Israel agrees to reopen Rafah only for Gaza pedestrians
Meanwhile, Israel said it would only allow pedestrians to travel through the Rafah crossing between Gaza and Egypt as part of its "limited reopening" once it has recovered the remains of the last hostage in the Palestinian territory.
Reopening Rafah, a vital entry point for aid into Gaza, forms part of a truce framework announced by Mr Trump in October, but the crossing has remained closed since Israeli forces took control of it during the war in the Palestinian territory.
Visiting US envoys had reportedly pressed Israeli officials to reopen the crossing during talks in Jerusalem over the weekend.
World leaders and aid agencies have repeatedly pushed for more humanitarian convoys to be able to access Gaza, which has been left devastated by more than two years of war and depends on the inflow of essential medical equipment, food and other supplies.
Prime Minister Benjamin Netanyahu's office said that Israel had agreed to a reopening "for pedestrian passage only, subject to a full Israeli inspection mechanism".
The move would depend on "the return of all living hostages and a 100% effort by Hamas to locate and return all deceased hostages", it said on X.
It remained unclear whether the reopening would allow medical patients to leave Gaza for treatment in Egypt or other countries.
The Israeli military said it was searching a cemetery in Gaza on Sunday for the remains of the last hostage, Ran Gvili.
"Upon completion of this operation, and in accordance with what has been agreed upon with the US, Israel will open the Rafah Crossing," said Mr Netanyahu's office.
The announcement came after Gaza's newly appointed administrator, Ali Shaath, said the crossing would open "in both directions" this week.
