Ri stressed that the the "declaration of war" means that all options will be on the table for the North Korean leadership.
"The whole world should clearly remember it was the US who first declared war on our country," Ri said to reporters in New York as quoted by Reuters.
He went on by stating that Trump declared war on North Korea by claiming the DPRK's "leadership would not be around much longer." Trump made the aforementioned comment in response to Ri Yong's UN General Assembly speech.
The development comes as US bombers flew in the international airspace off the North Korean eastern coast. Chief Pentagon spokeswoman Dana White said the move was made to showcase US military options available to Donald Trump.
The tensions between Pyongyang and Washington have been escalating recently over Pyongyang's nuclear test. North Korea has been continuously performing missile launches and nuclear tests, all conducted in violation of UN Security Council resolutions. The most recent test was made on September 15, when North Korea launched a ballistic missile, which flew over Japan before falling into the northern Pacific some 20 minutes after the launch.