The offensives "resulted in the severe suffering and hardship to tens of thousands of civilians sheltering in the interior at the time," the report said.

Indonesia, fearing a leftist takeover in East Timor following the end of Portuguese colonial rule in 1975, invaded the territory in late 1976 and annexed it.

The report said the U.S. felt compelled to support Indonesia's military government. That support included that of the Jimmy Carter Administration in the U.S., from 1977 to 1981, which had made protection of human rights a centrepiece of its foreign policy, the report noted.

Efforts to reach Richard Holbrooke, a former UN ambassador, who served as the Carter Administration's top official for East Asia, were unsuccessful.

Successive U.S. Administrations consistently stressed "the overriding importance of the relationship with Indonesia and the supposed irreversibility of the Indonesian takeover", the report said.

The report was prepared by East Timor's Commission for Reception, Truth and Reconciliation. Copies were distributed by the Washington-based National Security Archive, a research institute on international affairs. In preparing the report, East Timorese officials received assistance from foreign governments, including the U.S, and non-governmental organisations.

The study said U.S. officials generally declined to acknowledge the culpability of the Indonesian military for the large number of fatalities in East Timor.

"Instead," the report said, "they maintained that the deaths were due to drought, an argument that the commission finds to have been without merit". East Timor was granted independence from Indonesia in May, 2002. The report noted U.S. President Bill Clinton in 1999 persuaded Indonesia to accept the deployment of an Australian-led international force on East Timor to help end "massive" rights violations in the territory committed by Indonesian forces and pro-Jakarta groups.

In so doing, he demonstrated the "considerable leverage" that the U.S. could have exerted earlier had the will been there, the study said. The Commission for Reception, Truth and Reconciliation also claimed Indonesian soldiers intentionally killed five foreign journalists, including two Australians, reporting on the 1975 invasion of the East Timor town of Balibo.