SYDNEY (Reuters) - Australia will reiterate its opposition to the death penalty at a United Nations drugs conference, a government spokesman told Reuters, a move likely to ratchet up pressure on Indonesia as it prepares to execute two Australian drug smugglers.

Australia's Assistant Minister for Health Fiona Nash plans to "restate Australia's long-standing and firm opposition to the death penalty" in a speech to the UN's Commission on Narcotic Drugs on Monday, Ms Nash's spokesman told Reuters in an e-mail.

The planned executions of Myuran Sukumaran, 33, and Andrew Chan, 31, have raised diplomatic tensions between Australia and Indonesia after repeated pleas for mercy on their behalf. They are part of a group of up to 11 convicts, mostly foreigners, due to be executed on the prison island of Nusakambangan.

Ms Nash's speech at a meeting in Vienna will not mention Indonesia, the spokesman added, but it will add to the country's increasingly vocal complaints about Indonesia's treatment of the two Australian men after they were taken to the island shackled and under heavy guard.

Last Monday, Australian Prime Minister Tony Abbott said the government summoned Indonesia's ambassador to Australia to express "dismay" at "the undignified, at times almost macabre way that those two Australians were treated as part of the transfer".

"It is not in accordance with Indonesia's best values to execute these people who have been thoroughly rehabilitated and reformed," Mr Abbott told Australian media.

Last Friday, a spokesman for the UN High Commissioner for Human Rights urged Indonesia to "refrain from executing individuals convicted of drug offences" by granting clemency.

"Indonesia's relentless efforts to fight the scourge of drug trafficking are understandable, but this is not the way to do it," the spokesman Rupert Colville said.

By giving the death penalty to foreign nationals found guilty of drug trafficking, "Indonesia sadly will weaken its own position when advocating for its own nationals who sometimes face the death penalty abroad", Mr Colville added.