"The DPRK's measures for bolstering the nuclear force to the maximum will be taken in a consecutive and successive way at any moment and any place decided by its supreme leadership," according to the statement, carried by the state news wire Korean Central News Agency.

The North has long justified its nuclear weapons development as a deterrence against what it calls US hostility, and the recent pledges mean it will continue its nuclear and ballistic missile tests.

The North had been widely speculated to conduct a nuclear test in April, during which two of the country's key national events fall -- the birthday of North Korean founder Kim Il-sung and the anniversary of the formation of its military.

As the speculation sparked security jitters, the US has sent a strike group led by aircraft carrier USS Carl Vinson and nuclear-powered submarine USS Michigan to waters off the Korean Peninsula.

The Trump administration also unveiled its North Korea policy line last month, which vowed to step up sanctions and engagement to get the North to give up its nuclear program.

In the statement, the North accused the US of escalating tensions on the peninsula with the naval deployment and military threats.

"The US aggression hysteria has never reached such a height and the situation on the Korean Peninsula has never inched close to the brink of nuclear war as in the period of the recent drills," according to the KCNA.

"The DPRK is fully ready to respond to any option taken by the US ... (it) will continue to bolster its military capabilities for self-defense and preemptive nuclear attack with the nuclear force as a pivot," it noted.

If North Korea had not had nuclear capabilities, "the US would have committed without hesitation the same brigandish aggression in Korea as what it committed against other countries," it said, apparently referring to the recent US air strike on Syria. (Yonhap)