Japan will likely go nuclear if a unified Korea decides to keep the nuclear arsenal developed by North Korea, setting the stage for a tense military competition between the two Northeast Asian rivals, Yonhap News Agency reported Monday, quoting a U.S. congressional report.

"Any eventual reunification of the Korean Peninsula could further induce Japan to reconsider its nuclear stance," the report by the Congressional Research Service was quoted as saying.

"If the two Koreas unify while North Korea still holds nuclear weapons and the new state opts to keep a nuclear arsenal, Japan may face a different calculation," said the Jan. 19 report, titled "Japan's Nuclear Future: Policy Debate, Prospects and U.S. Interests." It cites some Japanese analysts as describing a nuclear-armed unified Korea as "more of a threat than a nuclear-armed North Korea."

Many Koreans still harbor resentment of Japan over its colonization of the Korean Peninsula for nearly four decades from 1910. Hundreds of thousands of Korean women were forced to serve as sex slaves for Japanese soldiers and millions of Koreans were taken to forced labor camps.

"If the closely neighboring Koreans exhibited hostility toward Japan, it may feel more compelled to develop a nuclear weapons capability," the report said, stressing the need for the U.S. to take into account Japan's possible nuclear armament in drawing up "U.S. contingency planning for future scenarios on the Korean Peninsula."

Japan is said to be a quasi-nuclear weapons state with ample plutonium for the production of warheads and advanced technology in the field.

"Japan's technological advancement in the nuclear field, combined with its stocks of separated plutonium, have contributed to the conventional wisdom that Japan could produce nuclear weapons in a short period of time," the CRS report said.