UN Secretary-General Ban Ki-moon lead worldwide condemnation of the assassination of Pakistan election candidate Benazir Bhutto decribing it as an "assault on stability" in Pakistan.
"I strongly condemn this heinous crime and call for the perpetrators to be brought to justice as soon as possible," Mr Ban said in a statement.
The 15-member UN Security Council went into closed session to discuss the killing. A formal statement is expected which current council President Marcello Spatafora of Italy said would "underline what the international community cannot accept,".
But he said the council would not be "meddling internally" in Pakistan's affairs.
President Mary McAleese expressed her shock and sadness at Ms Bhutto's death, and the other victims of the tragedy. "On my own behalf and on behalf of the people of Ireland, I send my deepest condolences to her family and to the people of Pakistan," she said.
Taoiseach Bertie Ahern said he was deeply shocked by the "appalling" attack and hoped the democractic process would not be affected.
India, Pakistan's giant neighbour and rival, said the assassination was a terrible blow to the democratic process.
"In her death the subcontinent has lost an outstanding leader who worked for democracy and reconciliation in her country," said a spokesman for Prime Minister Manmohan Singh.
The US, which sees Pakistan as a key ally in its battle against al Qaeda, had championed Ms Bhutto as a popular leader who might help return the country to a civilian-led democracy after nearly a decade of military rule.
"The United States strongly condemns this cowardly act by murderous extremists who are trying to undermine Pakistan's democracy," President George W Bush said in a statement.
He praised Ms Bhutto's courage in returning to Pakistan in October to participate in elections aimed at restoring a democratic government.
"She knew that her return to Pakistan earlier this year put her life at risk. Yet she refused to allow assassins to dictate the course of her country," Mr Bush said.
British Prime Minister Gordon Brown said the killing was a "sad day for democracy" and a "tragic hour for Pakistan".
"Benazir Bhutto may have been killed by terrorists, but the terrorists must not be allowed to kill democracy in Pakistan," he said.
French President Nicolas Sarkozy called the killing odious. "France, like the European Union, is particularly attached to stability and democracy in Pakistan," he said in a letter to Pakistan's President Pervez Musharraf.
Agencies