North Korea: Warnings and insults

North Korea's leader Kim Jong Un holds a meeting of the ruling party's presidium. Photo / AP

North Korea's foreign minister warned that a strike against the US mainland is "inevitable" because US President Donald Trump mocked leader Kim Jong Un with the belittling nickname "Little Rocket Man".

US bombers escorted by fighter jets flew off the North Korean coast in a show of force shortly before Foreign Minister Ri Yong Ho strode to the podium to address the United Nations General Assembly in New York, capping an extraordinary week of militaristic threats from both nations before an organisation founded to maintain international peace and security.

Ri said that Trump's bombast had made "our rockets' visit to the entire US mainland inevitable," and linked it to the Trump's insulting shorthand references to Kim. Trump responded on Twitter: "Just heard Foreign Minister of North Korea speak at UN. If he echoes thoughts of Little Rocket Man, they won't be around much longer!"

Harsh sanctions placed on North Korea's trade with the outside world will have no impact on its ability to complete building a nuclear bomb capable of reaching the United States, Ri said. "Through such a prolonged and arduous struggle, now we are finally only a few steps away from the final gate of completion of the state nuclear force. "

The rhetoric between Trump and Kim has grown exceptionally personal. At a rally on Saturday in Alabama, Trump called Kim "Little Rocket Man," magnifying the disparaging label he slung at King in his UN speech last Wednesday in which he threatened the United States would "totally destroy" North Korea in defence of itself or its allies. He said Kim was on "suicide mission". Kim in turn called Trump a "frightened dog" and a "mentally deranged US dotard". Ri echoed those sentiments, calling the President a "mentally deranged person full of megalomania" and at one point referring to him "President Evil". Ri added: "None other than Trump himself is on a suicide mission".

Tensions are escalating so quickly that when an 3.5 magnitude earthquake was detected in northern North Korea on Saturday night in the vicinity of a nuclear test site, it briefly aroused suspicions that North Korea had conducted another underground nuclear test. It was quickly confirmed as just an earthquake.

A US B-1B Lancer bomber prepares to take off from Guam. Photo / AP

The Pentagon disclosed that the US Air Force B-1B Lancer bombers flew in international airspace east of North Korea. The Pentagon said it was the farthest point north of the Demilitarised Zone separating North and South Korea that any US planes have flown in this century. The bombers took off from an air base in Guam, which North Korea has threatened to target. They were escorted by F-15C fighter jets from Okinawa, Japan.