North Korean Foreign Minister Ri Yong Ho said Saturday his country will take "merciless pre-emptive action" if there is any sign of a U.S. military attack on it, while deriding U.S. President Donald Trump as being on a "suicide mission."

Ri sounded the warning in a speech at the U.N. General Assembly in response to Trump's labeling earlier this week of North Korean leader Kim Jong Un as "Rocket Man" on "a suicide mission" and his threat to "totally destroy" the country.

(United Nations)

He said Pyongyang will take "merciless pre-emptive action in case the U.S. and its vassal forces show any sign of conducting a kind of 'decapitating' operation on our headquarters or military attack against our country."

"Due to his lacking of basic common knowledge and proper sentiment, he tried to insult the supreme dignity of my country by referring it to a rocket," he said of Trump.

"By doing so, however, he committed an irreversible mistake of making our rocket's visit to the entire U.S. mainland inevitable all the more," he said. "None other than Trump himself is on a suicide mission."

North Korea's top diplomat also called Trump a "mentally deranged person full of megalomania and complacency" who is trying to turn the United Nations into a "gangsters' nest."

"The person who is chastised even by American people as 'Commander in Grief,' 'Lying King,' 'President Evil' is holding the seat of the U.S. president," Ri said, adding that Trump will be held "totally responsible" if innocent Americans are harmed.

"Trump might not have been aware what is uttered from his mouth, but we will make sure that he bears consequences far beyond his words, far beyond the scope of what he can handle even if he is ready to do so," he said.

Ri's remarks came a day after Kim threatened to take the "highest-level" of retaliatory action against Trump, which Ri said "could be the most powerful detonation of an H-bomb in the Pacific Ocean."

In defiance of U.N. Security Council resolutions, North Korea on Sept. 3 conducted its sixth and largest nuclear test, saying it was a hydrogen bomb that can be mounted on an intercontinental ballistic missile.

There is increasing speculation that Pyongyang may carry out yet another provocative act around the founding anniversary of its ruling Workers' Party of Korea on Oct. 10.

Ri said North Korea's nuclear arsenal is "to all intents and purposes, a war deterrent for putting an end to nuclear threat of the U.S. and for preventing its military invasion."

He also said sanctions will have no effect on Pyongyang's resolve to develop nuclear weapons, noting the "ultimate goal is to establish the balance of power with the U.S."

The U.N. Security Council unanimously adopted a resolution toughening sanctions against Pyongyang in response to its latest nuclear test.

Trump also announced Thursday new unilateral U.S. sanctions taking aim at North Korea's weapons programs by sanctioning banks, other entities or individuals that trade with the country.

"Now we are finally only a few steps away from the final gate of completion of the state nuclear force," the minister said. "It is only a forlorn hope to consider any chance that (North Korea) would be shaken an inch or change its stance due to the harsher sanctions by the hostile forces."

After the U.N. speech, Ri met with U.N. Secretary General Antonio Guterres, who voiced concern over the escalating tension and called for Pyongyang's compliance with Security Council resolutions banning the North from engaging in nuclear and missile activities, a statement released by the world body said.

Guterres also emphasized the need for a "political solution" to the Korean Peninsula crisis and for continued humanitarian assistance to the North, according to the statement.

In a show of force, the U.S. Defense Department said earlier in the day that U.S. Air Force bombers escorted by fighters flew in international airspace over waters east of North Korea.

"This mission is a demonstration of U.S. resolve and a clear message that the President has many military options to defeat any threat," Pentagon spokeswoman Dana White said in a statement.

"We are prepared to use the full range of military capabilities to defend the U.S. homeland and our allies," she added.