An estimated 500,000 people were killed during a purge of Communists - or those deemed to have had links to communism - by the Indonesian government.

On September 30, 1965 the Communist Party of Indonesia, the PKI, was accused of orchestrating a failed coup by the then-leader of the army, General Suharto.

Six army generals were murdered, and what followed was the targeted killing of anyone deemed to be communist.

Over the next few months into 1966, at least 500,000 people were killed by the army and local militia groups.

The victims included members of the PKI, ethnic Chinese, as well as trade unionists, teachers, activists, and artists.

The Indonesian government has argued that the killings were justified because the communists attempted a coup as part of their attempt to make Indonesia a communist state.

The International People's Tribunal on 1965 Crimes Against Humanity in Indonesia has looked into the events of 1965 and 1966.

Over a period of four days in November, the panel of judges held public hearings in The Hague, and have now released their findings.

Presiding judge Zak Yacoob, a former South African Constitutional Court Justice, says there is no doubt crimes against humanity and war crimes took place.

"All these acts were an integral part of a broad, widespread, systematic attack against the Partai Komunis Indonesia - the PKI Communist Party of Indonesia - its affiliate organisations, its leaders, members, supporters and their families, as well as those seen to have been sympathetic to its aims, as well as supporters sympathetic to Sukarno's supporters and of course, more broadly, against people who've had no connection to the PKI in what became a widespread purge, which included many supporters of President Sukarno and many supporters of the Partai Nasional Indonesia."

He says the Indonesian government is responsible.

"The acts of mass killing and all other associated immoral crimes in 1965 and subsequently, and the failure to prevent their occurrence or to take action against their perpetrators, occurred under the full responsibility of the State of Indonesia. Senior members of the Indonesian government have acknowledged that these crimes were committed, but few have expressed a desire to investigate them or apologise for them."

The Tribunal's findings say other crimes against humanity - including inhumane imprisonment, enslavement, torture and sexual violence - also took place.

Zak Yacoob says the United States, Britain and Australia were complict in facilitating the wrongful acts of mass killings and other crimes against humanity.

"There is abundant evidence provided to the tribunal that within a few weeks after 30 September (1965), the governments of the United States, United Kingdom, and Australia were well aware through reports from their own diplomats in Jakarta, as well as from foreign media and some non-government observers, that the communists and many others accussed of association with them were being slaughtered on a large scale. By the beginning of 1966, the numbers that were being reliably reported to Washington, London and Canberra ranged from a minimum of 100,000 to four times that count."

The report also accuses Australia of running what it describes as a sophisticated propaganda operation.

"The UK and Australia conducted a sustained campaign repeating false propaganda from the Indonesian army, and they continued with this policy even after it had become abundantly clear that killings and other crimes against humanity were taking place on a mass and indiscriminate basis. On balance, this justifies the charge of complicity in the above crimes against humanity."

Justice Yacoob says the report makes several recommendations.

"This report calls upon the Indonesian government urgently and without qualification to a) apologise to all victims, survivors and their families for the commission by the State of all the crimes against humanity and other crimes committed in Indonesia in relation to the 1965 events; b) investigate and prosecute all crimes against humanity; c) ensure appropriate compensation and reparation to victims and survivors."

The tribunal heard from the prosecutors, as well as from more than 20 witnesses.

The judges also received several hundred pages of documents, tendered as evidence.

Indonesia did not participate in the hearings.

Australia, Britain and the US also didn't take part in the proceedings which took place in The Hague over four days between November 10 to November 13.