A U.S. scientist says South Korea could be tempted to develop its own nuclear weapons to cope with a nuclear-armed North Korea or if Japan decides to go nuclear.

Charles Ferguson, president of the Federation of American Scientists, made the claim in a report, saying external geopolitical and internal domestic political circumstances could lead to "trusted allies, such as South Korea or Japan" developing nuclear weapons.

"If the United States were perceived to not be able to reliably and credibly counter the threats posed by China and North Korea, prudent military planners in Japan and South Korea would want to take steps to have their own nuclear capabilities," Ferguson said.

"Finally, if Japan crosses the threshold to nuclear weapon acquisition, South Korea would feel compelled to follow suit. South Korean leaders would then not want to be vulnerable to both nuclear-armed North Korea and Japan," he said.

The scientist also claimed that South Korea is capable of making 2,500 kilograms, or 416 bombs' worth, of "near-weapons-grade plutonium" from four pressurized heavy water reactors (PHWRs) at its Wolsong power plant.

"Once South Korea has at least a few bombs' worth of plutonium and has confidence in its missile systems, it could go for a quick breakout that would most likely be used to signal North Korea, China, Japan and the United States," Ferguson said in the report.

"One plausible purpose of this signaling of these initial 'diplomatic' bombs would be to prod Washington as well as Beijing to engage seriously on the denuclearization of North Korea," the report said.

South Korea could then leverage its base of a handful of nuclear bombs and implement its potential to make dozens of nuclear warheads annually from near-weapons-grade plutonium produced from its four PHWRs, he said.

"The initial steps could take place conceivably within a five-year period," he said.

Ferguson also claimed that the HANARO research reactor at the Korea Atomic Energy Research Institute in the central city of Daejeon could also be used to produce up to 11 kilograms of weapons-grade plutonium annually if operated at full power.

The scientist cautioned, however, that his intention is not to argue for South Korea's acquisition of nuclear bombs, adding that the best option for South Korea and Japan at the moment is for the U.S. to continue to demonstrate its resolve to provide conventional and nuclear extended deterrence. (Yonhap)