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(CNN) —  

North Korean leader Kim Jong Un said the country would not use a nuclear weapon unless its sovereignty is encroached by “invasive hostile forces with nuclear weapons,” according to the country’s state news agency KCNA.

He made the remarks Saturday at the ruling Workers’ Party of Korea’s Seventh Congress in Pyongyang, which began the day before.

Kim also reportedly said North Korea will faithfully fulfill its nuclear nonproliferation obligations and make an effort to realize global denuclearization.

In his 15-minute opening speech Friday, Kim touted the country’s weapons development, saying they had “elevated our respect to the world and enemies.”

In January, Pyongyang announced that it had successfully tested a thermonuclear device, which, if true, would mark a significant advance in its nuclear capabilities.

It has since made a number of public demonstrations of its nuclear program’s advancement, including rocket and submarine-based missile tests. It also announced it had miniaturized a warhead in early March.

Kim called on the country to push forward “the building of nuclear force and boost self-defensive nuclear force both in quality and quantity,” according to KCNA.

Julia Mason, a State Department ‎spokeswoman, said the U.S. called on North Korea to “suspend all activities related to its nuclear and ballistic missile programs and to abandon them in a complete, verifiable and irreversible manner.”

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North Korea’s ‘golden age?’

Kim also said during his opening remarks that the congress would review the party’s “brilliant successes” and put together tasks to “keep ushering in a great golden age of socialist construction.”

The country’s provocative nuclear stance has triggered some of the harshest U.N. sanctions imposed against North Korea and irritated his most powerful ally, China.

The sole remaining symbol of cooperation with South Korea – the Kaesong Industrial Complex near the demilitarized zone – has also shut down during his tenure.

No Chinese officials were invited to the party congress, according to Chinese state media.