"We estimate that the nuclear testing program in the Marshall Islands will cause about 500 additional cancer cases among Marshallese exposed during the years 1946-1958, about a nine percent increase over the number of cancers expected in the absence of exposure to regional fallout," the NCI study said.

The study said because of the young age of the population when exposed in the 1950s, more than 55 percent of cancers have yet to develop or be diagnosed.

The NCI completed the study in September last year but it was only publicly released last week after officials from the Marshall Islands noticed a reference to it in a US Congressional report and requested a copy.

It was prepared for the US Senate Committee on Energy and Natural Resources, which is scheduled to launch hearings next month to review a petition from the Marshall Islands seeking more than US$3 billion in additional compensation for nuclear test damages and health care.

At the time of the Bravo test at Bikini Atoll, US officials played down the health implications for islanders.

Bikini Islanders were not evacuated despite their land's being engulfed in snow-like radioactive fallout for two-to-three days after the Bravo bomb, which was equivalent to 1,000 Hiroshima bombs.

Although many islanders developed severe radiation burns and had their hair fall out as their land was engulfed in fallout, US Atomic Energy Commission authorities issued a statement following the test saying "there were no burns" and the islanders were in good health.

US officials later allowed islanders to return home to live in radioactive environments without performing any cleanup work on their islands.

The US paid US$270 million in a compensation package in the mid-1980s part of which went to the Majuro-based Nuclear Claims Tribunal.

But the tribunal says only a limited amount was made available for payouts and has described the original settlement as "manifestly inadequate."