North Korea claimed Wednesday that it has manufactured nuclear warheads small enough to fit on the head of a missile, an announcement that is likely to rachet up tensions in east Asia, particularly with South Korea. 

According to Yonhap News, a spokesman for North Korea's National Defense Commission said that the development of the alleged weapons was part of an initiative to boost Pyongyang's self-defense capability.

"It is long since the DPRK's nuclear striking means have entered the stage of producing smaller nukes and diversifying them," the spokesman said, using the acronym of North Korea's official name, the Democratic People's Republic of Korea. "The DPRK has reached the stage of ensuring the highest precision and intelligence and best accuracy of not only medium- and short-range rockets, but long-range ones."

If the North's claim is true, it presents a fresh threat to the security of South Korea and Japan, as well as the United States. Pyongyang has previously claimed that it has the technology to build a nuclear weapon small enough to fit on an intercontinental ballistic missile, which could reach the U.S. mainland. 

The statement comes days after North Korea claimed that it had successfully test-fired a submarine-launched ballistic missile earlier this month. South Korea had downplayed that announcement, characterizing the exercise as a test ejection, rather than a firing. South Korean officials believe the missile only traveled approximately 110 yards after it left the water, Yonhap reported.

The South Korean assessment was supported Tuesday by Navy Adm. James Winnefeld, vice chairman of the Joint Chiefs of Staff, who told an audience at a Washington think tank that North Korea was "years away" from developing the capability to launch ballistic missiles from submarines. 

The U.S.-Korea Institute at Johns Hopkins University in Baltimore raised its own questions about the viability of North Korea's claimed test, saying that images released by Pyongyang may have been altered and raising the possibility that the missiles were launched from a submerged barge instead of a submarine.

However, U.S. and South Korean officials appear to have acknowledged that North Korea carried out a test of some kind. On Tuesday, Winnefeld said that if North Korea develops the capability of launching ballistic missiles from a submarine, "it will present a hard-to-detect danger for Japan and South Korea as well as our servicemembers stationed in the region."

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