executed an Australian drug trafficker just before dawn on Friday
despite repeated pleas by Australia's government for clemency,
sending a chill over relations between the long-time allies.
Nguyen Tuong Van, 25, was hanged at the city-state's Changi prison just after 6.00 am local time. A minute after the execution, a large church bell in Nguyen's home city of Melbourne tolled 25 times - once for every year of his life.
The hanging follows weeks of campaigning by his lawyers, his family and civil rights groups to stop the execution.
Thousands of people gathered in Australia to pray and mourn for Nguyen in the final 24 hours of his life while Singapore activists moved in pairs overnight to light candles at the prison. Public gatherings of more than four people require a police permit in the tightly-controlled city-state.
"I hope the strongest message that comes out of this...is a message to the young of Australia - don't have anything to do with drugs, don't use them, don't touch them, don't carry them, don't traffic in them," Australian Prime Minister John Howard told Australian radio.
Australia, a staunch opponent of capital punishment, ditched diplomacy this week and called the hanging a "barbaric" act.
About 70 people, including Australian politicians, gathered outside the Singapore High Commission in Canberra on Friday with a banner reading "Oh Singapore, how could you?" while protesters clutching flowers rallied in Sydney and Melbourne.
In a tiny concession to Australia, Singapore's prison authority allowed Nguyen to hold hands with his mother before his execution but rejected pleas to let them have a final hug.
"She said to me she was talking to him and able to touch his hair and face. It was a great comfort to her," Nguyen's lawyer Julian McMahon told reporters outside the prison, which was crowded with reporters and onlookers.
Nguyen's twin brother Khoa and a family lawyer arrived at the prison at dawn. They could not witness the execution but said they wanted to be as close as possible to Nguyen when he died.
His mother, Kim Nguyen, was in a Singapore chapel with friends, praying for her son.
Analysts said short-term relations between the countries would be strained because of the execution, but said Singapore would not likely budge on its mandatory death sentence for crimes such as murder, firearms offences and drug trafficking.
"Singapore is a small, affluent society next door to one of the world's biggest suppliers of drugs, the golden triangle. I think Singapore would have been a very different place if it was not tough on it," said political analyst Seah Chiang Nee.
But activists said that while the campaign to abolish the death penalty would be an uphill battle, they would continue to fight against the "gruesome, state-sanctioned murder".
Singapore is one of Australia's strongest allies in Asia and Howard has rejected calls for trade and military boycotts.
Singapore activists, along with the family of a man who was executed in May, arrived before the hanging holding a picture of Nguyen with a yellow and white garland to condemn the execution.
"What do we get out of this? What do we get out of this murder?" M. Ravi, a human rights lawyer said outside the prison.
A private funeral service will be held in Singapore on Friday afternoon. The family is due to return to Australia on Saturday evening. Nguyen's body will be flown to Australia for burial.
Australia last hanged someone in 1967. The death penalty was abolished by states during the late 1960s, early 1970s.