North Korea said Wednesday that it has already secured the technology to make nuclear warheads small enough to fit on a missile, further escalating tensions sparked by its recent test-firing of a submarine-launched ballistic missile.

In a statement, a spokesman for the North's powerful National Defense Commission said it will defend the North with the nuclear weapons made small enough to be mounted on missiles, Yonhap news agency reported.

The statement came as the North recently claimed that it successfully test-fired a ballistic missile from a submarine.

Experts have raised concerns over Pyongyang's move, since it is seen as part of efforts to equip its missiles with miniaturized nuclear bombs.