Ri Yong Ho told reporters in New York: 'The whole world should clearly remember it was the U.S. who first declared war on our country. 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.
South Korean analysts believe, though, the US measure wouldn't target North Korean diplomats.
North Korea strengthens its military on the eastern coast in response to US.
The National Intelligence Service (NIS) has confirmed that North Korea did not take any response measures when U.S. B-1B Lancer bombers flew in worldwide airspace off North Korea's eastern coast last Saturday.
Lee quoted the NIS as saying that the North later tightened its surveillance along the east coast.
"Since the United States declared war on our country, we will have every right to make countermeasures, including the right to shoot down United States strategic bombers even when they are not inside the airspace border of our country".
"This past weekend, Trump again declared war on us, saying that our regime will not last long", Ri said, saying that the worldwide community had hoped for the war of words between Washington and Pyongyang to escalate into actions. "The world must remember clearly that it was the USA that first declared war on us".
Mr Ri, who made his remarks before leaving NY following last week's UN General Assembly, added: 'In light of the declaration of war by Trump, all options will be on the operations table of the supreme leadership of the DPRK (Democratic People's Republic of Korea)'.
But White House spokesman Sarah Sanders on Monday denied the United States had declared war, calling the suggestion "absurd".
South Korea, meanwhile, continues to seek means to ease tension between Washington and Pyongyang. Pyongyang says it needs those programs as a deterrent against hostility by the USA and its regional allies, including South Korea and Japan.