The Taoiseach Mr Ahern and his British counterpart Mr Tony Blair today discussed the appointment of a judge to probe a string of high profile murders in Northern Ireland.
The two governments have agreed an investigation is needed into six killings, including lawyers Rosemary Nelson and Pat Finucane.
Both Mrs Nelson and Mr Finucane were killed by loyalist paramilitaries in retaliation for their representation of nationalists in the province.
Relatives have attacked the plan to appoint a judge to oversee the investigation as a stalling tactic.
However, speaking in Downing Street after the meeting, Mr Ahern said "an eminent international judge" was needed.
"We had some discussions about the kind of person we want but it has to be someone experienced in the area of human rights and large investigations," he said.
He and Mr Blair also discussed Northern Ireland and the forthcoming European Union summit during a working lunch at No 10.
The Taoiseach had played down the significance of the meeting which was also attended by the Northern Secretary, Dr John Reid and the Minster for Foreign Affairs Mr Cowen. He said the leaders did not want to "put any undue temperature" on it.
The leaders welcomed "progress" being made by the Northern Ireland executive under the leadership of the First and Deputy First Ministers, Downing Street.
They had been expected to discuss the general political situation, including the decommissioning of terrorist arsenals, progress towards demilitarisation and the approaching political marching season.
They also considered preparations for the EU summit in Barcelona next month but No 10 refused to give details.
Mr Ahern also raised Irish concerns over the nuclear waste disposal complex at Sellafield, Cumbria, a spokeswoman confirmed.
Dublin claims the site amounts to an environmental and pollution threat and a potential terrorist strike target, but No 10 refused to give details of Mr Blair's response.
Meanwhile Sinn Fein sources tonight indicated party leader Mr Gerry Adams will meet Mr Ahern in Dublin on Wednesday.
A party source said: "The discussions will focus on policing which requires an awful lot of work but also demilitarisation, criminal justice reform and the implementation of the Good Friday Agreement."
PA