North Korea warned Tuesday that it won't hesitate to use nuclear weapons against the United States and its allies if they continue with their "hostile" foreign policy.

"If the U.S. and other hostile forces persistently seek their reckless hostile policy towards the DPRK and behave mischievously, the DPRK is fully ready to cope with them with nuclear weapons any time," said the director of the North's Atomic Energy Institute, according to the state-run Korean Central News Agency (KCNA), reported CNN.

Of particular concern to the North are annual military drills conducted in the area by the U.S. and South Korea. In late August, troops stages their biggest-ever joint live-fire drill, which included a stimulated assault deep into North Korean territory, reported AFP.

The North Korean energy official said that the country's primary nuclear complex at Yongbyon, which contains a uranium enrichment plant and a plutonium production reactor, is now fully operational.

"All the nuclear facilities in Yongbyon [Nuclear Scientific Research Center], including the uranium enrichment plant and five megawatt reactor were rearranged, changed or readjusted and they started normal operation," he said, according to RT.

Pyongyang is improving its nuclear weapons arsenal "in quality and quantity," he said, adding, scientists are making "innovations day by day" to "guarantee the reliability of the nuclear deterrent ... as required by the prevailing situation," reports the Daily Mail.

He continued: "In the meantime, the US anachronistic hostile policy toward the DPRK that forced it to have access to the nuclear weapons has remained utterly unchanged and instead it has become all the more undisguised and vicious with the adoption of means openly seeking the downfall of the latter's social system."

North Korea has become notorious for threatening to attack the U.S., especially in times of diplomatic strife. But most experts agree that it probably doesn't have the technology to send a missile to the U.S. mainland.

The declaration comes a day after the isolationist nation announced it is planning to launch a series of satellites aboard long-range rockets in honor of next month's 70th anniversary of the ruling Workers' Party of Korea, as HNGN reported.