"Thanks to our reliable and effective self-defensive nuclear deterrent, there will no longer be war, and our country's safety and future will be firmly guaranteed forever."
North Korea's state media only described the suspected patient as a person who had "run away" to South Korea three years ago before returning to the North.
Kim Yo Jong, the sister of North Korean leader Kim Jong Un, said last week that another summit between him and Trump was unlikely this year, but "a surprise thing may still happen."
Kim Yo Jong, the sister of North Korea's leader, came a day after the US point man for North Korea, Deputy Secretary of State Stephen Biegun, wrapped up a three-day visit to Seoul.
"We do not feel any need to sit face to face with the US, as it does not consider the DPRK-US dialogue as nothing more than a tool for grappling its political crisis," the FM said.
North Korean leader Kim Jong Un presided over a video conference meeting of the ruling party's Central Military Commission, where members "took stock of the prevailing situation."
"Never again will we provide the US chief executive with another package to be used for achievements without receiving any returns," he said. "Nothing is more hypocritical than an empty promise."
For several days, North Korea has lashed out at South Korea, threatening to close an inter-Korean liaison office and other projects if the South does not stop defectors from sending leaflets.
The two-day meeting comes at a time of economic uncertainty amid the global COVID-19 pandemic that is putting additional pressure on the North's economy, already battered by international sanctions.
North Korea says it has no confirmed cases of the new coronavirus, but South Korea's intelligence agency has said it cannot rule out that the North has had an outbreak.