The eight men executed in Indonesia overnight recited the Lord's Prayer and worshipped God in the moments before their deaths, witnesses say.

Pastor Karina de Vega, who was assigned to counsel Nigerian prisoner Okwudili Oyatanze – dubbed "The Death Row Gospel Singer" and one of those executed on Nusakambangan Island in the early hours of Wednesday morning – told the Sydney Morning Herald that the prisoners sang 'Bless the Lord O My Soul' and 'Amazing Grace' as they were lined up, bound to crosses, to face the firing squad.

All eight refused blindfolds; choosing to look their executioners in the eyes. Their worship was cut short by gunfire.

"They were praising their God," Vega said of the prisoners' final moments. "It was breath-taking. This was the first time I witnessed someone so excited to meet their God."

She added that the eight bonded together, like brothers, and sang "one song after another...like in a choir.

"The non-Christian, I believe, also sang from his heart. It was such an experience," she said.

Irish-born priest Father Charlie Burrows, who was also present on Nusakambangan Island, has told reporters that he and other spiritual advisors were told to wait in a nearby tent while the executions took place. He said they joined the inmates – all of whom were convicted of drug trafficking – in song.

"The good thing is all prisoners were executed together while praying and singing. Before that they hugged each other, saying goodbye," Christina Widiantarti, a lawyer for the Brazilian convict – Rodrigo Muxfeldt Gularte – and a witness to the execution, told Reuters.

An official confirmed that the men were shot at 12.35am local time, as their families prayed and recited the Lord's Prayer outside. "We didn't think it would happen," Father Burrows told the Sydney Morning Herald. "It is finished. It's all done."

The Indonesian government has defended its decision to go through with the executions, despite international pressure to grant clemency. "We are fighting a war against horrible drug crimes that threaten our nation's survival," Attorney General Muhammad Prasetyo told reporters.

"I would like to say that an execution is not a pleasant thing. It is not a fun job, but we must do it in order to save the nation from the danger of drugs. We are not making enemies of countries from where those executed came. What we are fighting against is drug-related crimes."

Two of those executed, Australians Andrew Chan and Myuran Sukumaran, gained particular media attention in the days leading up to their deaths. They were given just 72 hours' notice of their impending sentence on Saturday and the Australian government intervened, warning Indonesian president Joko Widodo about the diplomatic repercussions of the execution. The World Council of Churches also urged Widodo to reconsider.

Prime Minister Tony Abbott has now branded the executions "cruel and unnecessary" and withdrawn Australia's ambassador from Indonesia.

"We respect Indonesia's sovereignty but we do deplore what's been done and this cannot be simply business as usual," he told reporters in Canberra.

"I want to stress that this is a very important relationship between Australia and Indonesia but it has suffered as a result of what's been done over the last few hours."

The hashtag #boycottIndonesia began trending in Australia as news of the deaths spread.

Religious leaders have also spoken out against the death penalty in the lead up to the executions. Brian Houston, senior pastor of Hillsong Church, was in almost daily contact with Chan before his death. Chan was convicted of co-leading a heroin smuggling operation known as the 'Bali Nine' along with Sukumaran but converted to Christianity while in prison. He studied theology, and was ordained a minister earlier this year. He married his fiancée, Febyanti Herewila, two days before his execution.

In a post online yesterday, Houston said it had been a great privilege to get to know Chan and Sukumaran in recent months. "By all accounts, these two young men...have not only accepted the mercy and forgiveness of Jesus Christ, but have also rehabilitated themselves to be upstanding members of the prison system," Houston wrote.

"Even in jail they have made a positive contribution to the lives of other prisoners, and sought to pay their debt to society. I have had the pleasure of speaking with Andrew Chan almost every day and his faith and strength under extreme duress, have inspired me."

He included a screenshot of a message from Chan, in which the prisoner refers to Matthew 6:7, which encourages Christians not to worry, and says: "It's not easy to love our enemies and those who persecute us but what good is a testimony without the test in it?"

"Drugs are a destructive social weapon, and their prevalence in this day and age must be a focus of our efforts for change. Trafficking of drugs must be a condemned behaviour – something that both Andrew and Myuran understand more than ever – but not one with such absolute and irreversible consequences," Houston continued.

"In the world, power is understood as a show of authority, irrespective of opposing views – yet, Jesus model of power was one of humility and grace. God has pardoned us all, he has and continues to extend grace to our wrongdoings. Extending grace is not a sign of weakness, but of believing in life and in people."

In a post on his Facebook page, Australian activist Jarrod McKenna said he was deeply moved by Chan's message to Houston.

"This is the power of the Gospel. The power to transform drug dealers into pastors of inmates. The power to show mercy to those who are offering no mercy. The power to love your enemies even while they are planning to execute you," he wrote.

"In Australia tonight, I can think of no more poignant witness to the way of the Cross, the way of enemy-love, the way of trusting in Resurrection. Let's continue to make a stand against the death penalty and pray for Andrew and Mayuran."

The bodies of the Australians will be flown back to their home country for burial. Sukumaran's sister, Brin, posted on Facebook: Bless the lord o my soul . Myu likes this song . He sang it today . Please sing it for him .