North Korea claimed on Wednesday that it has been able to secure technology that will allow it to create nuclear warheads small enough to fit on a missile, South Korea's Yonhap News Agency reported.
The announcement is likely to exacerbate tensions following the North's apparent test-firing of a ballistic missile from a submarine earlier this month, Yonhap said.
However, The Guardian reported that analysts and a U.S. Navy admiral believed images showing the launch were faked.
Admiral James Winnefeld told an audience at the Centre for Strategic & International Studies (CSIS) in Washington on Tuesday that he thought Pyongyang was still "many years" from having submarine-launched missiles.
However, a spokesman for the secretive state's National Defense Commission said in a statement released by the official Korea Central News Agency Wednesday that the North would protect itself with nuclear weapons made small enough to be mounted on missiles, Yonhap reported.