The official Pentagon statement included the likelihood of a biological and chemical weapon defense by the People's Democratic Republic of Korea (DPRK), and was penned by Rear Admiral Michael Dumont, vice director of the Pentagon's Joint Staff.
House members Ted Lieu of California and Ruben Gallego of Arizona, both Democrats, requested the information.
The Pentagon made that assertion in a letter to lawmakers who wanted to know about the logistics and human cost of any conflict with North Korea.
"Their assessment underscores what we've known all along: there are no good military options for North Korea", the statement said.
He also pointed out that Seoul, the South's capital with a population of 25 million, is just 35 miles from the demilitarized zone.
Thae, who is making his first visit to Washington since his defection previous year, said the US and allied South Korea would win a war after a preventive military strike on the North, but there would be a "human sacrifice" inflicted on the South from the "tens of thousands" of artillery guns and short-range missiles the North has at the frontier.
The letter was published as Donald Trump begins his mammoth tour of Asia, during which the North Korean threat is expected to be a major topic of discussion.
They also said the Trump administration 'has failed to articulate any plans to prevent the military conflict from expanding beyond the Korean Peninsula and to manage what happens after the conflict is over'.
A t a speech Sunday at Yokota Air Base in Fussa, Japan, Trump rallied the American service members and assured USA allies in the region that he had their backs in the face of the rogue regime's threats.
Trump kicked off a 12-day Asian trip and is looking to present a united front with Japan against North Korea through meetings with Prime Minister Shinzo Abe amid heightened tensions over Pyongyang's nuclear and missile tests.
He said: "What's inflammatory is the North Korean regime and what they're doing to threaten the world".
Korea's continuing efforts to expand its missile and nuclear weapons programs will be a main topic. It was not pleasant for them, was it? The situation worsened when Trump, during his first address to the United Nations General Assembly (UNGA), vowed to annihilate North Korea if it posed any threat to the USA and its allies, and called the Pyongyang leader "rocket man" on a suicide mission.
" Together with our allies, America's warriors are prepared to defend our nation using the full range of our unmatched capabilities, said Trump, who was wearing a military-style bomber jacket".