Kim Jong Un
North Korean leader Kim Jong Un reacts after the test-fire of a new cruise rocket in this undated photo released by North Korea's Korean Central News Agency (KCNA), May 30, 2017. Reuters

Just days after reports surfaced the U.S. and South Korea would discuss North Korea's demands in order to end its nuclear program, Pyongyang's state media said Sunday its "self-defensive nuclear deterrent force is never subject to any kind of negotiations."

North Korea has vowed to continue developing its defensive capabilities amid the reclusive country's concerns the U.S. and South Korea will start a war. Kim Jong Un's regime has claimed its continued missile tests have been in retaliation to Washington and Seoul's joint military drills in the Korean Peninsula.

Read: North Korea Conducts ICBM Rocket Test, But Could Take Time To Have Missile Ready

"We should make every effort to strengthen our national defense with the nuclear capability as the backbone," North Korea's official newspaper Rodong Sinmun said in an editorial, according to Yonhap News. "If South Korea truly wants to improve the Korean ties and seek peace, it should stop picking on our nuclear deterrent force and stand against the U.S.'s plot for first nuclear strike on the North."

On Thursday, North Korea carried out another test of a rocket engine as part of the program developing an intercontinental ballistic missile (ICBM), which is capable of carrying a nuclear warhead, and reaching the U.S. mainland. However, experts believe Pyongyang is far from developing a missile that could hit Washington.

North Korea has been conducting missile launches, amid increasing tensions in the Korean Peninsula despite receiving tough sanctions and warnings from the United Nations.

In return, North Korea warned the U.S. about its recent military drills with South Korea as well as its missile defense system, the Terminal High Altitude Area Defense system (THAAD), installed in South Korea in April. North Korea has accused the U.S. of escalating tensions with its actions and refers to its own missile launch tests as measures to safeguard its country, while Washington believes the joint military drills with Seoul are important to safeguard against any North Korean threat.

“By relentlessly bringing in a number of strategic nuclear assets to the Korean peninsula, the U.S. is gravely threatening the peace and safety and driving the situation to the brink of nuclear war,” North Korean officials said in a statement in April. “This has created a dangerous situation in which thermo-nuclear war may break out at any moment.”

On Tuesday, President Donald Trump posted a tweet stating China’s efforts to threaten North Korea to scale back the expansion of their nuclear weapons program has not worked so far.

"While I greatly appreciate the efforts of President Xi & China to help with North Korea, it has not worked out. At least I know China tried!" Trump wrote.

Hours after the president sent out the tweet, Secretary of State Rex Tillerson and Defense Secretary Jim Mattis met with Chinese Secretary of State Yang Jiechi, and a member of the Chinese Central Military Commission Gen. Fang Fenghui, to discuss the North Korean issue.