North Korea said on Tuesday that it was ready to use nuclear weapons against the United States and announced that it has restarted operations at its atomic bomb fuel production plants.

Pyongyang's state-run Korean Central News Agency (KCNA) quoted the director of the North Korean Atomic Energy Institute, who said that the regime was improving its nuclear weapons arsenal "in quality and quantity," CNN reported.

"If the [United States] and other hostile forces persistently seek their reckless hostile policy towards the [Democratic People's Republic of Korea] and behave mischievously, [North Korea] is fully ready to cope with them with nuclear weapons any time," the source threatened.

The country's main nuclear complex at Yongbyon, which includes a uranium enrichment plant and a plutonium production reactor, is operating normally, the unnamed official told the newswire.

The threat came amid speculations that Pyongyang might mark the 70th anniversary of the founding of the country's ruling Workers' Party on Oct. 10 by showcasing its nuclear capabilities, the New York Times added. Dictator Kim Jong-un "is believed to count the North's arsenal of nuclear weapons and missiles as one of the proudest achievements of his family," which has ruled the country since 1948.

North Korea on Monday also announced it was preparing to launch a new satellite into orbit for scientific purposes, even though the United States has urged the regime to refrain from doing so. Washington and its allies fear such launches may be a cover for developing an intercontinental ballistic missile.

But, "the world will clearly see our rocket fly high at a time and a place that the North's party will set," KCNA predicted.

South Korea's defense ministry said the launch would be a "serious provocation," and would constitute both a military threat and a violation of U.N. resolutions, the South Korean news agency Yonhap reported, according to USA Today.

"South Korea and the United States are jointly watching for all possibilities with regard to North Korea's [potential] long-range missile launch," the ministry's spokesman, Kim Min-seok, said in a briefing. But "so far, no particular signs have been seen," Kim cautioned.