The US Air Force has flown its B-1B Lancer bombers, escorted by F-15 jet fighters, off North Korea’s coast “farthest north of the Demilitarized Zone,” in what the Pentagon describes as a show of “US resolve” while Pyongyang’s top diplomat insists at the UN that targeting US mainland with missiles is “inevitable.”

"This mission is a demonstration of US resolve and a clear message that the president has many military options to defeat any threat," Pentagon spokeswoman Dana White said on Saturday. "We are prepared to use the full range of military capabilities to defend the US homeland and our allies."

She was further quoted by Reuters as saying, "This is the farthest north of the Demilitarized Zone (DMZ) any US fighter or bomber aircraft have flown off North Korea’s coast in the 21st century, underscoring the seriousness with which we take (North Korea’s) reckless behavior."

According to the report, the warplanes took off from Okinawa, Japan and flew over the waters east of the Korean Peninsula.

The provocative flight on Saturday by the American warplanes was disclosed just hours before North Korea’s Foreign Minister Ri Yong Ho was to address the United Nations’ annual General Assembly meeting, during which he referred to US President Donald Trump as "a mentally deranged person full of megalomania and complacency" and accused him of trying to turn the world body into a "gangsters’ nest."

Calling Trump “President Evil,” Ri further went on to vow that Pyongyang was prepared to defend itself if the US showed any sign of conducting a "decapitating operation on our headquarters or military attack against our country."

"Now we are finally only a few steps away from the final gate of completion of the state nuclear force," North Korea’s top diplomat also told the annual gathering of world leaders.

Ri’s speech capped a week of growing tensions between Washington and Pyongyang, with US President Donald Trump and North Korean leader Kim Jong Un exchanging insults. Trump called Kim a "madman" on Friday, a day after Kim referred to him as "mentally deranged US dotard."

Ri then insisted that Trump himself was on a "suicide mission" after the US president had alleged that Kim was on such a mission, further underlining that US-led sanctions would have any effect on Pyongyang’s resolve to develop its nuclear program, with the ultimate goal stated as "balance of power with the US."

Trump announced the new US sanctions on Thursday, pointing out that they allow targeting of companies and institutions that finance and facilitate trade with North Korea.

Earlier this month, the UN Security Council unanimously adopted its ninth round of sanctions on Pyongyang to counter its nuclear and ballistic missile programs.

The flight of US warplanes off the North Korean coast followed a 3.4 earthquake registered in the country on Saturday, which prompted fears of a new nuclear test. The seismic event, however, turned out to be a natural occurrence and “unlikely man-made,” according to geology and nuclear weaponry experts.