The Taoiseach has expressed his "shock and outrage" at the murder of Kenneth Bigley in Iraq today, while Prime Minister Tony Blair condemned the "barbaric nature" of the killing, from his country retreat.
Speaking this evening from the Asia / Europe Summit in Vietnam, the Taoiseach said this "callous murder of an innocent man is a most shocking and brutal outrage".
"The perpetrators have shown a total lack of mercy and humanity and in doing so have reached new depths of barbarism, " the Taoiseach said.
"I am profoundly saddened by this murder of an Irish citizen and my deepest sympathy and the sympathy of the Irish people are with his mother, Elizabeth, his wife and family at this sad time."
Prime Minister Blair has expressed his "utter revulsion" over the death of the Liverpool-born engineer and said those who resorted to hostage-taking around the world must not be allowed to win.
"I feel utter revulsion at the people who did this, not just at the barbaric nature of the killing but the way frankly they played with the situation over the past few weeks," Blair told reporters. "I feel a strong sense, as I hope others do, that the actions of these people whether in Iraq or elsewhere should not prevail over people like Ken Bigley".
The Minister for Foreign Affairs, Mr Dermot Ahern, said he was "profoundly shocked and saddened" at the killing.
In a statement posted on the department's website this evening, Mr Ahern added: "I am desperately disappointed that all our efforts and pleadings for mercy and humanity to be shown to Kenneth went unanswered.
"I want to extend, on my own behalf and that of the Government, my most sincere condolences to his mother and to his family, whose courage and fortitude we came to know and admire over recent weeks. Our thoughts and prayers are with them at this tragic time, as are those of all Irish people, at home and abroad.
"I strongly deplore this cruel and barbaric act, and call for an immediate end to the inhumane practice of seizing and killing hostages in Iraq."
President McAleese has also expressed her shock and sadness to learn of Mr Bigley's death.
"Despite the best efforts of all those who endeavoured to secure his safe release from captivity, Mr Bigley has been cruelly taken from his loved ones. My deepest sympathies are with the Bigley family who have conducted themselves with immense dignity during a period of unimaginable distress and heartache.
"I join with the people of Ireland today in extending my most sincere condolences to the family on their profound loss," added President McAleese.