Indonesia's defence minister said Thursday suspected communists killed in 1960s military-backed massacres "deserved to die", as a backlash mounts against efforts to resolve one of the darkest chapters in the country's history.

Hardline ex-general Ryamizard Ryacudu made the comments to a gathering of former military figures and nationalist groups convened in response to moves by the government to come to terms with the mass killings.

Rights groups have called for an official apology for the massacres, in which at least 500,000 people died, but Ryacudu noted that US President Barack Obama did not say sorry for the nuclear bombing of Hiroshima on a recent trip to Japan.

"Millions of people died because of the bomb, and that was war," he said, adding that those killed in the 1960s massacres had mounted an "uprising" so the victims "deserved to die".

His comments were greeted with applause by the hundreds attending the event.

The massacres began after General Suharto put down a coup blamed on communists in 1965, and over several months local militias backed by the military carried out one of the worst mass killings of the 20th century.

An anti-communism group holds a rally in Bandung, West Java province, Indonesia on August 21, 2015 Bima Shakti, AFP/File

Suharto rose to power on the back of the bloodshed and during his 32-year rule it was presented as necessary to rid the country of communism, debating the killings publicly was taboo, and no one was ever held to account.

Calls have mounted for the killings to be re-examined since the dictator's 1998 downfall. In April the government took some steps, backing for the first time a series of discussions into the killings and announcing it would exhume sites that activists say are mass graves.

However Ryacudu and conservative elements of the security forces have pushed back. There has been a wave of arrests in recent weeks of people accused of spreading communism, which remains illegal in Indonesia.

Agus Widjojo, who led the government-backed discussions into the massacres, disagreed with Ryacudu's comments and insisted an apology should be made to everyone affected by the massacres.

"An apology needs to be given to those who suffered from human rights abuses during that period," he said.