Reuters –  Australia made a last-minute plea on Monday for a stay in the imminent execution of two Australian drug traffickers in Indonesia, saying reports that their trial had been tainted by corruption needed to be investigated.

The call from Foreign Minister Julie Bishop almost immediately deepened a diplomatic row with Jakarta.

Bishop said the allegations that judges requested money to commute the death sentences for the pair were "very serious" and called into question the integrity of the sentencing process.

Indonesia's foreign ministry hit back, saying Australia needed to show proof of alleged corruption and questioned why concerns were being raised only now instead of 10 years ago.

Armanatha Nasir, spokesman for Indonesia's foreign ministry, said Australians Myuran Sukumaran and Andrew Chan had been given all the legal avenues to challenge their death sentences.

The two are among nine drug convicts, including others from Brazil, Philippines, Ghana, Nigeria and Indonesia, who are due to be executed by firing squad as soon as Tuesday night.

Stepping up pressure to save a Filipina mother of two who says was duped into carrying drugs, the Philippines' president appealed to Indonesian President Joko Widodo at a summit of Southeast Asian nations for "humanitarian consideration".

In what appeared to be the first sign of softening from Widodo, he told his counterpart he was sympathetic and would consult with the attorney general on the case, a spokesman for Philippines President Benigno Aquino said in Kuala Lumpur.

Indonesia has harsh punishments for drug crimes and resumed executions in 2013 after a five-year gap. Widodo has been unbending in his hard line on traffickers and his refusal to grant foreigners on death row clemency has strained relations with several countries, particularly neighbor Australia.

The nine are being held at a high-security jail on Nusakambangan Island in central Java, where dozens of police and military personnel started tightening security on Monday, erecting barriers and keeping the public at a distance.

A local undertaker, Suhendro Putro, said he had handed nine coffins over to the police on Sunday.

"I cannot say they are for those prisoners but I've been called for a meeting today at the port to prepare. I don't know when exactly the executions will happen," he said.

Chan and Sukumaran, ringleaders of the so-called Bali Nine, were arrested at the main airport on the holiday island of Bali in 2005 for trying to smuggle 8 kg (17.6 lb) of heroin to Australia. The other members of the gang, all Australians, have been jailed for between 18 years and life in Indonesia.

Bali-based lawyer Muhammad Rifan told the Sydney Morning Herald that he had agreed to pay judges in the cases of the two men more than A$130,000 ($101,647) to give them a prison term of less than 20 years.

Rifan said the deal fell through when the judges told him they had been ordered by senior legal and government members in Jakarta to impose a death penalty and he didn't have enough money to meet a revised, higher demand for a lighter sentence.

"It's a matter for Indonesia's Judicial Commission to investigate these matters and that underlines why we continue to request Indonesia to allow the judicial commission to finalize its review," Bishop told reporters.

"An execution is an irrevocable step and I believe that these hearings and these appeal processes should be concluded before any decision is taken."

Rifan could not be reached for comment.

Indonesia's Judicial Commission said it would look into reports alleging corruption but said its findings would have no bearing on their cases.

"Even if it is proven that the judge violated ethical codes, it won't affect the court's earlier decision," Commissioner Taufiqqurahman Syahuri told Reuters.

"We cannot annul a decision from a court, such a thing can only be done by a higher court. What has been decided is final. The Judicial Commission can punish the judge, but ethical and legal matters are different."

Bishop criticized Indonesia for informing Chan and Sukumaran of their imminent execution on April 25, a day when Australians remember their war dead, particularly poignant this year given the 100th anniversary of what is now known as ANZAC Day that marks the start of a doomed World War One campaign in Turkey.

"I'm very disappointed that it proceeded in this way," she said, adding that it was not too late for Widodo to have "a change of heart" and stay the executions.

Indonesia also fired back on Monday at calls over the weekend by U.N. Secretary-General Ban Ki-moon not to execute the nine and declare a moratorium on capital punishment.

"Fifteen executions also took place in the backyard of the U.N. between January and April but there was no comment or statement by the secretary-general," Foreign Ministry spokesman Nasir said. "That is one reason why President Jokowi (has) ... called again for the urgent reform of the U.N. to ensure it works for all its members and not just a few."

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