North Korea has moved its airplanes and strengthened defences on its eastern coast after the US dispatched fighter jets and bombers to the Korean peninsula earlier last weekend, a South Korean intelligence source said on Tuesday.

A spokesperson for the National Intelligence Service (NIS) told Efe news that this information, which was transmitted to a parliamentary committee by a member of the intelligence services, was yet to be confirmed.

The US aircraft, which according to the Pentagon, have reached the closest point to North Korean territory for the first time in recent years, were sent off to North Korea around midnight on Saturday.

The North Korean military was unable to detect the B-1B and F-15 jets flying near its coast due to a possible failure of its military's radar system, Intelligence Committee Chairman Lee Cheol-woo told Yonhap News Agency.

The time at which the US was carrying out its operation might have been the reason why North Korean radars did not work properly over the power supply problems in the Communist country, NIS added.

The North Korean military is believed to have an immediate warning system for possible airborne intrusions with a detection range of up to 600 km.

The US bombers' dispatch came after the leaders of both countries, Donald Trump and Kim Jong-un, engaged in an intense verbal conflict, which, with Pyongyang's constant weapons tests, has greatly escalated the tension in the region.

North Korean Foreign Minister Ri Yong-ho also staged the latest episode of the verbal war in New York on Monday, after saying that the US President's statement to the UN, in which he threatened to "totally destroy North Korea", was a declaration of war against his country.