Donald Trump’s Secretary of Defense, General James “Mad Dog” Mattis, has warned North Korea that any attack on the United States would lead to a retaliation that is both “effective and overwhelming.”

In a visit to South Korea to affirm U.S. support in the region, Mattis said that “North Korea continues to launch missiles, develop a nuclear weapons program and engage in threatening rhetoric and behavior.”

“Any attack on the United States or our allies will be defeated and any use of nuclear weapons would be met with a response that would be effective and overwhelming,” he continued.

According to statements on the call from both nations before his visit, Mattis promised South Korean Defense Minister Han Min Koo that the United States would support Seoul “against the evolving North Korean threat.”

“Our new administration inherits a very strong, trusted relationship between our two countries, and it’s our commitment to make it even stronger,” Mattis said this week.

“There is no other nation that needs to be concerned about THAAD other than North Korea if they’re engaged in something that’s offensive,” he continued, adding that Pyongyang’s seemingly ceaseless “provocative behavior” could not remain unanswered.

During his election campaign, President Donald Trump criticized America’s contribution to both South Korea and Japan for defense, saying both countries needed to pay more for military protection.

A report released this week on North Korea’s Yongbyon nuclear facility indicates that Pyongyang has restarted its plutonium reactor, possibly in an attempt to generate enough fuel for a nuclear bomb.

The country also carried its fifth nuclear test last September, receiving condemnation from the international community. Following Trump’s election in November, North Korea’s government said that they “do not care” about his victory and that it would have no impact on any government policy.

On Friday, it was reported by South Korean authorities that North Korea, last month, sacked their state security chief presumably over corruption charges.

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