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.
North Korea has reportedly stiffened its perimeter defences along the east coast, deploying ballistic missiles as well as additional ground forces and anti-aircraft batteries.
Speaking on the sidelines of the United Nations General Assembly on Saturday, North Korean Foreign Minister Ri Yong-ho said that his country could carry out a nuclear bomb test over the Pacific if the U.S. continued to threaten the country.
Speaking at the General Assembly on Tuesday, US President Donald Trump denounced North Korea's leader as a "Rocket Man" who is on a "suicide mission". We are prepared to defend ourselves and our allies from an attack and are prepared to use the full range of capabilities at our disposal against the threat from North Korea.
There also existed the risk that obsolete North Korean interceptor aircraft could have crashed during a night flight, he added.
In a letter to global leaders on Sunday, a North Korean parliamentary committee said Trump's threat constitutes a declaration of war against Pyongyang.
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"These words were uttered by the incumbent president of the U.S., therefore it is a clear declaration of war".
"We have not declared war on North Korea and frankly the suggestion of that is absurd" White House press secretary Sarah Huckabee Sanders said.
One South Korean expert said that Pyongyang could have detected the B-1B Lancer, but would not have had a clear image of the plane.
According to South Korea's Yonhap news agency, the U.S. revealed the aircraft's flight path intentionally and North Korea is preparing for another American show of force.
"It is imperative that we, Korea and the United States together, manage the situation, in order to prevent further escalation of tensions or any kind of accidental military clashes which can quickly go out of control", South Korean Foreign Minister Kang Kyung-wha said in a speech in Washington, while warning that Pyongyang was likely to carry out more provocations.