As nine convicted drug traffickers prepare for their planned execution tonight, the general secretary of the World Council of Churches (WCC) has urged the Indonesian president to grant clemency.

"Your country's decision to resume executions sets Indonesia against the global trend towards abolition of the death penalty," Rev Dr Olav Fykse Tveit wrote in a letter to President Joko Widodo. Indonesia abolished the death penalty in 2008, but re-established it in 2013. Five foreign nationals and an Indonesian were executed for drug trafficking in January of this year.

"I join the many others around the world who have appealed to you for clemency for the death row prisoners scheduled to be executed imminently," Tveit continued. "Despite the crimes of which they have been convicted, these sisters and brothers are all children of God, created in God's own image.

"I support this appeal out of respect for the precious unique value of every human life, and for the God-given dignity of every human being – even those who have committed serious crimes against their fellow human beings and against society."

His letter follows an appeal made by Bishop Ketut Waspada of the Christian Protestant Church in Bali, who also wrote to the President, urging him to stop tonight's execution.

"Let us ask ourselves deep in our hearts: do we, as human being, really have the authority to take the lives of other people?" Waspada asked.

"I think only God has the authority to continue or to end the lives of His creations. So our lives are in God's hands. With the death-sentenced it means that we take over God's authority. It also means that we do not give a chance to that person to change his or her life into a better one, since he or she has the right to live. It means that the death-sentenced is contradictory with human rights."

The bishop drew attention to the two Australians among those set to die tonight: Andrew Chan and Myuran Sukumaran. They were convicted in 2006 of co-leading a heroin smuggling operation from Indonesia to Australia, known as the 'Bali Nine' and sentenced to death by firing squad.

In prison, Chan converted to Christianity and began leading the English language church service, studying theology and becoming an ordained Christian minister. He was endorsed by five senior ministers form different denominations in Australia after having spent years studying Christianity from his cell.

Speaking of the moments after his original sentencing, Chan has said: "When I got back to my cell, I said, 'God, I asked you to set me free, not kill me.' God spoke to me and said, 'Andrew, I have set you free from the inside out, I have given you life!' From that moment on I haven't stopped worshipping Him. I had never sung before, never led worship, until Jesus set me free."

Christie Buckingham, a senior pastor at Bayside Church in Melbourne visited Chan to ordain him, and later told the Sydney Morning Herald: "I have never experienced a student like Andrew, and probably never will again. He is extraordinary. He has such a determination to learn, in fact almost a desperation.

"He is the real deal, and Myuran [Sukumaran] is as well. They are living proof that people can change, circumstances can change. Indonesia should be proud of the impact they are having."

Chan has helped other prisoners to get over their drug addictions, and even led some to faith. Former inmate Matius Arif Mirdjaja was baptised by Chan in prison, and has spoken of his devotion to Christianity - the two set up a Bible study together. Mirdjaja now preaches at churches around south-east Asia, but visits Chan regularly when he is in Bali.

Sukumaran too has been described as a model prisoner by guards, and began painting in prison. He gained bachelor of fine arts through Melbourne's Monash University and began teaching classes to other inmates. Together with Chan, he set up a drug rehabilitation programme.

"These guys have love and compassion and a genuine heart," Mirdjaja said of the two Australians. "[Their] message is simple - love and compassion. They never judge other people."

Both Chan and Sukumaran have launched multiple appeals and the Australian government has intervened but Indonesian authorities have so far not relented. The prisoners were given 72 hours' notice of their death sentence on Saturday and their relatives visited today to say their last goodbyes.

Representatives from both families later gave statements urging president Widodo to show mercy. "There has to be a moratorium on the death penalty, no family should endure it. Because now the family is going to have a grieving process for the rest of their life," Chan's brother, Michael, told reporters this afternoon.

"I just hope the president, somewhere in his heart, he can find the courage to show some mercy to these nine individuals and call this off, because it's not too late. It's up to him."

Reports surfaced earlier today that the Indonesian government had denied Chan and Sukumaran their choice of ministers to counsel them in their final hours. Sukumaran had asked for Buckingham, while Chan requested David Soper, a Salvation Army officer and family friend. According to the latest reports, however, the government has now relented on the matter. Buckingham and Soper are expected to witness the executions.

Though no official time has yet been given, Sukumaran's mother, Raji, told press that it will happen around midnight. Marked coffins have already been prepared for all nine of the prisoners.

Australian minister for foreign affairs Julie Bishop said today: "Short of a last-minute intervention by President Widodo I fear the very worst for our citizens."