The Good Friday Agreement is the best way forward for Northern Ireland's political process, the Irish prime minister has said.
Mr Ahern said he welcomed the opening of dialogue with the DUP
Bertie Ahern said if a better way ahead was available for the British and Irish Governments and political parties, it would already have been found.
He said he was "absolutely convinced" the Agreement was the only instrument to achieve a lasting settlement.
In a keynote address at the University of Ulster's Coleraine campus on Thursday, he stressed that this meant republicans bringing the definitive closure to paramilitarism as well as inclusive partnership.
He said there can be no halfway house between violence and democracy.
However, in a message to unionists he said they must sign up to the "imperative of total partnership based on inclusion of all parties whose electoral mandate gives them a right to participation".
Mr Ahern committed his government to breaking the political impasse.
"I believe we can meet this challenge," he said.
"The road already travelled has indeed been
long and winding and we cannot and must not stop now."
He said direct rule was not the preferred option of most people in Northern Ireland.
He also said other aspects of the Agreement should be implemented, including equality and normalisation.
Mr Ahern said he welcomed the opening of dialogue with the DUP.
"Our recent meeting in London was positive. It was a good start. We are committed to continuing these contacts with them at all levels. It has taken many years to get to this point.
"But I believe that open and honest engagement will allow us to confirm to them that the Irish Government are honourable and fair-minded partners in this indispensable process.
"At the same time, we want to continue our work with loyalist leaders, to create vibrant and confident loyalist communities, that are stakeholders in the new era of partnership on this island.
"We recognise their difficulties and challenges in leaving behind the negative agenda of the past and we commend the ongoing efforts of those who are trying to lead people out of the cul-de-sac of paramilitarism."
During his one-day visit to Northern Ireland, Mr Ahern laid a wreath at the scene of the Omagh bombing in memory of those who died.
Mr Ahern travelled by helicopter between engagements throughout the province on Thursday.
Although the taoiseach has made frequent trips to Northern Ireland for political discussions, this type of visit is a rarer occurrence.
Earlier, Mr Ahern met SDLP leader Mark Durkan before travelling to Coleraine.
He then headed to Omagh for his first visit since he attended a prayer service in the County Tyrone town shortly after the August 1998 Real IRA bombing.
Mr Ahern met local politicians and relatives of people killed and injured in the bombing, which was the single worst atrocity in 30 years of violence in Northern Ireland.
Some relatives, including Michael Gallagher whose 21-year-old son Aidan died in the bomb, stayed away in protest at what they saw as the "token" nature of the visit.
Mr Ahern will visit the scene of the Omagh bombing which killed 29 people
Michael Gallagher, spokesman for the relatives, said: "We have been asking for a meeting with him for five years, but when I asked how long we would be able to meet with him, I was told the most we could hope
for was five to 10 minutes."
He added: "We want a proper sit-down meeting, not a photo opportunity for the Taoiseach."
Instead, they travelled to Dublin for a meeting with Enda Kenny, the leader of the main Irish opposition party, Fine Gael.
Mr Ahern rounded off his trip in Belfast, meeting the city's Lord Mayor, Martin Morgan, as well as councillors and community workers.
BBC Northern Ireland political editor Mark Devenport said such a trip might have been considered a "security nightmare" in the past.
But following recent contacts between Mr Ahern and loyalists as well as talks with the DUP, Irish Government officials said no major protests were expected.