There has been strong condemnation in both Northern Ireland and the Republic of the murder of Sunday World reporter Mr Martin O'Hagan.
The Taoiseach, Mr Ahern, said: "Those responsible for this barbarous act have no place in the new society all right-thinking people are trying to build in Northern Ireland. They have deprived a family of a husband and a father for no other reason than to satisfy their craven thirst for violence."
The Northern Secretary, Dr John Reid, described the killing as "barbaric". "It shows contempt for human life, contempt for the freedom of the press, and contempt for the people of Northern Ireland."
The Ulster Unionist Party leader, Mr David Trimble, denounced the murder as cowardly.
The SDLP leader, Mr John Hume, said he was "absolutely stunned" by the murder. "It is an appalling murder and an attack on the whole community and the democratic process."
Sir Reg Empey and Mr Seamus Mallon, the acting First and Deputy First Ministers in the Northern Ireland Assembly, in a joint statement described Mr O'Hagan's murder as "an attack on democracy itself". Sinn FΘin's Mr Martin McGuinness said the murder was "deplorable".
The chairman of the Ulster Democratic Party, Mr John White, said there was no justification for the murder. However, he said Mr O'Hagan had made enemies of many loyalists.
The National Union of Journalists (NUJ) has called on workers in all media organisations to observe a one-minute silence at 2 p.m. today as a mark of respect. The union has also opened a book of condolences which will be open all day today in Liberty Hall, Dublin.
The Sunday World, which produced a special memorial edition yesterday, said in a statement: "The cold-blooded murder of our friend and colleague Martin O'Hagan was an appalling attack on freedom of expression and democracy. He was a member of a Sunday World news team in Northern Ireland which were fearless in their pursuit of democracy and the peace process.
"His death marks a new low point for freedom of expression and his passing casts a shadow over the basic civil liberties every decent person treasures."
Mr Gavin O'Reilly, chief executive of Independent News and Media (Ireland), which owns the Sunday World, said he was shocked and horrified by the murder. "Martin's murder will only galvanise all those opposed to terrorism in every form and strengthen the determination to advance the forces of peace."
Mr Kevin Cooper, Belfast-based member of the NUJ's National Executive Council, said: "The protection of journalists covering Northern Ireland is of paramount importance to ensure that the public has a full range of opinion and knowledge of what is going on."
The co-ordinating director of the National Newspapers of Ireland, Mr Frank Cullen, said Mr O'Hagan's murder was an attack on the fundamental role of newspapers in society.