Declassified diplomatic cables from the 1960s reveal that the United States not only knew of the communist purge led by the Indonesian army then, but was also considering lending its support militarily.

This, in the event of an insurgency in Indonesia by the local communist party, better known as the PKI, elements of which were slaughtered in a genocide that has yet to be addressed fully by Jakarta today.

"If there is a reasonable possibility that the Indonesian army might request our help against a PKI insurgency, then I suppose it would not hurt to consider how we would respond," wrote Mr Norman Hannah, an adviser to the US Pacific Command, in a cable dated Oct 23, 1965.

In his report, Mr Hannah also said any request from the Indonesian army "might include anything from covert operations and assistance on up through the spectrum, including transport, money, communications equipment, or arms".

The cable sent to the US Embassy in Jakarta was among 39 declassified documents made public by the National Security Archive at George Washington University on Tuesday.

The documents, read by The Straits Times yesterday, were part of a collection of nearly 30,000 pages of embassy records, from 1964 to 1968, which covered the failed coup against then President Sukarno on Sept 30, 1965.

The Indonesian army blamed the rebellion on the PKI, accusing it of trying to wipe out the anti-communist leadership in the country.

It also led to retaliatory killings of possibly up to two million people linked to the PKI by the military and members of Muhammadiyah and Nahdlatul Ulama (NU) - two of Indonesia's largest Islamic groups.

Early estimates reported in a cable from the embassy's first secretary, Ms Mary Vance Trent, to the State Department on Dec 21, 1965, had put the number of deaths from the massacre at 100,000, but the killings would continue to be reported for months after that.

Ms Trent in an earlier cable, dated Dec 17, 1965, also observed "a widespread falsification of many documents, such as alleged confessions" of PKI members held by the Indonesian army in the capital.

Another cable, dated Oct 12, 1965, indicated that besides its knowledge of the ongoing massacre, Washington was aware that the army, under the command of then General Suharto, was planning to overthrow Sukarno.

The army "is now considering possibility of overthrowing Sukarno himself and is approaching several Western embassies to let them know that such a move is possible", reported Mr Marshall Green, then US ambassador to Indonesia.

Although the PKI was disbanded in 1966, Islamic nationalists in Indonesia continue to harbour a strong sense of paranoia and suspicion towards communism.

Just last month, the police clashed with a mob in downtown Jakarta protesting against what they had suspected was a gathering of the PKI. This was followed by a rally days later outside Parliament by Muslim hardliners who wanted to "block the resurrection of the PKI".

This recent resurgence of anti-communist sentiments has stoked fears that forces behind religion-and race-based attacks in domestic politics are moving to play the commie card against their reformist rivals in elections.

The declassified cables have reopened old wounds for Indonesians, many of whom remain divided over that dark period in their country's history and the purported "Red Scare".

Revelations in the documents, which include reports of how suspected communists were beaten up and executed after interrogation by the army, have unnerved many.

The complicity of members of Muhammadiyah and NU in some of the violence has also come as a shock for some.

In a Dec 6, 1965, cable, the Muhammadiyah branch in Medan, North Sumatra, was said to have distributed instructions for mosques to say that it was a religious obligation to kill the PKI, and "the shedding of whose blood is comparable to killing chicken".

These instructions, the cable's author added, were being interpreted as a "wide licence for killing", which was similar with the "final interpretation" of the NU leadership then.

Mr Asvi Warman Adam, a historian at the Indonesian Science Institute, yesterday said the actions of the two Islamic groups were caused by tensions between the communists and the Muslims at the time.

"Under today's context, such incidents would not happen, because Muhammadiyah and NU are now more moderate," he said.