Enda Kenny has condemned those responsible for a car bomb attack in the North that killed a policeman.
The Taoiseach described the bomb attack in Omagh, Co Tyrone, as a heinous and pointless act of terror.
"Those who carried it out want to drag us back to the misery and pain of the past," Mr Kenny said. "They are acting in defiance of the Irish people. They must know that they can never succeed in defeating the democratic will of the people."
Pc Ronan Kerr, 25, a Catholic recent recruit to the police service, was getting into his car on his way to work when the booby trap bomb exploded on Saturday afternoon.
President Mary McAleese said she was deeply shocked and saddened by the murder.
"This heinous crime will not succeed in its evil intent of destroying the peaceful and democratic future to which the people of Northern Ireland are so clearly committed," she added.
Tanaiste Eamon Gilmore said: "Those behind such violence have no mandate and are acting contrary to the democratic will of the people of Ireland, north and south."
Sinn Fein president Gerry Adams said his thoughts were with the family of the police officer at this traumatic time. "Sinn Fein is determined that those responsible will not set back the progress of the peace and political process," he added.
The blast will send shivers through the people of Omagh, where 29 people, including a woman pregnant with twins, were killed when a Real IRA car bomb exploded in the town in 1998.
Garda commissioner Martin Callinan said the loss of Pc Kerr was shared by the entire police family. "Tonight we in An Garda Siochana stand together with our colleagues in the Police Service of Northern Ireland," he said. "Our uniforms may be woven from different cloth but the police on this island are bound together by a shared resolve and determination to bring those responsible for this senseless crime to justice."