Story highlights The Pentagon urges North Korea "to refrain from provocative actions"

U.N. Security Council voted this week to impose sanctions against North Korea

Joint military drills between the United States and South Korea are set to take place soon

(CNN) For a second day, North Korea appeared to be flexing its military muscles in the wake of a United Nations vote meant to cripple the nation's nuclear program.

North Korean leader Kim Jong Un said the country's "nuclear warheads need to be ready for use at any time," the North Korean state news agency KCNA reported Friday.

"Under the extreme situation that the U.S. Imperialist is misusing its military influence and is pressuring other countries and people to start war and catastrophe, the only way for our people to protect sovereignty and rights to live is to strengthen the quality and quantity of nuclear power and realize the balance of power," Kim said, according to KCNA.

The news agency also confirmed the test-fire of a new multiple launch rocket system. It's unclear whether that event is the same launch by North Korea of "short-range projectiles," announced one day earlier by the South Korean Joint Chiefs of Staff.

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"We are aware of the reports. We are closely monitoring the situation on the Korean Peninsula in coordination with our regional allies," the Pentagon said in response to Friday's news. "We urge North Korea to refrain from provocative actions that aggravate tensions and instead focus on fulfilling its international obligations and commitments."

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