The Hermit Kingdom, referencing dictator Kim Jong Un, said an "outstanding leader" will determine the country's destiny.
Addressed to Democrat Congressmen Ted Lieu of California and Ruben Gallego of Arizona, the letter lays out the stark potential consequences of conflict with the rogue state, and says that North Korea could resort to using its stockpile of chemical and biological weapons.
At the very least, millions of people would die in this sort of war.
Increasing animosity would be a burden for Moon.
Alex Sigley, the runner of the Australian company, said: "It's a fascinating country, there's no other country in the world like North Korea".
"We remain postured to respond in the event of a provocation or conflict, and we have taken all appropriate measures to protect our allies, the Republic of Korea (ROK) and Japan, and U.S. Forces in those countries", the letter reads. "And that's very important to me", Trump told reporters. Many South Koreans are watching if Trump will make off-the-cuff remarks on the trade deal during news conferences or on Twitter. The White House later described the notion that the US had declared war "absurd".
South Korean presidential spokesman Park Soo-hyun speaks at a media briefing on U.S. President Donald Trump's upcoming state visit at Cheong Wa Dae on November 5, 2017. Security jitters subsequently flared among many in South Korea and Japan.More news: Outgoing Twitter employee deactivates Trump's account
The first Trump-Putin meeting in person was held on July 7 on the sidelines of the G20 summit in Germany's Hamburg.
South Korea now pays more than 900 billion won ($800 million) annually and negotiations with the United States are to start in the coming months to try to determine a new amount for South Korea to contribute.
While announcing the deal last week, Beijing, which views the Terminal High-Altitude Area Defense system as a security threat, said it noted that Seoul stated it won't do several things: deploying an additional THAAD battery, helping develop security cooperation with Japan and the US into a trilateral military alliance and joining a global USA missile defense network.
South Korea's Foreign Minister Kang Kyung-wha is interviewed by NBC News' Lester Holt.
The talks between Putin and Trump also come as critics of the USA president accuse the White House of slow-walking new sanctions against Russia imposed by Congress, which wanted to signal its displeasure with Russian interference in the 2016 election.
Despite the announcement, the sanctions are expected to have little impact on North Korea's illegal activities to fund its weapons programme as all trade and financial exchanges have been barred since May 2010 following the torpedoing of a South Korean warship by North Korea.