By Christine Kim

SEOUL (Reuters) – North Korea has warned that if the United States goes ahead with delayed military exercises with South Korea after the Winter Olympics it will not “sit idle”, the North’s foreign minister said in a letter to the United Nations.

North Korea has not tested a missile since late November 2017 and entered into inter-Korean dialogue in January, the first talks in two years, which have eased tensions after a year of escalating rhetoric between the Pyongyang and Washington.

Whenever joint military exercises took place “the peace and security of the Korean peninsula were gravely threatened and the inter-Korean mistrust and confrontation reached the top, thus creating great difficulties and obstacles ahead of hard-won dialogues,” North Korea’s Foreign Minister Ri Yong Ho said in the letter published by the official North Korean news agency.

“We will make every effort to improve inter-Korean relations in future, too, but never sit idle with regard to sinister act of throwing a wet blanket over our efforts.”

The United States and South Korea have agreed to push back a routine early-year joint military drill until after the South holds the Pyeongchang Winter Olympics and Paralympics. The Games begin next week and run until March 18.

In the letter, Ri said the United States was misleading public opinion by claiming its pressure campaign, including “their harshest sanctions,” had brought about the inter-Korean talks, when the “dramatic turning point” was entirely thanks to North Korean leader Kim Jong Un.

In a commentary on Friday, North Korea’s state media said Washington was attempting to create a “stage of confrontation” at the Olympics by saying that inter-Korean talks and positive results that had stemmed from them could “disappear” after the Games.

Asked to comment, a spokesman for the U.S. State Department, Mike Cavey, said: “The United States and our allies and partners in the region have long conducted routine exercises to maintain readiness. These exercises ensure we are trained for combined joint operations.”

U.S. President Donald Trump’s administration has warned that all options are on the table, including military ones, to resolve the crisis over North Korea’s development of nuclear weapons capable of hitting the United States.

While it has repeatedly said it prefers a diplomatic solution, Trump has exchanged threats with Kim and U.S. officials have said Trump and his advisers have discussed a preventative “bloody nose” strike on North Korea, alarming experts who warn that this could trigger catastrophic retaliation, especially on South Korea.

U.S. officials have said the debate on military action has lost some momentum as a result of the intra-Korean talks, which Trump has called a “good thing” and credited to his tough stance.

Joseph Yun, the U.S. special envoy on North Korea, said on Thursday he did not think the administration was close to triggering military action.

The White House said on Friday that Trump and Japanese Prime Minister Shinzo Abe spoke by telephone and discussed an expanded missile defense system and other efforts to boost Japan’s defenses amid the tensions over North Korea’s nuclear program.

Trump also spoke to South Korean President Moon Jae-in about human rights in North Korea and trade between the United States and South Korea, the White House said.

North Korea also criticized U.S. Vice President Mike Pence’s pending visit to the Olympics, accusing Washington of halting improvements in inter-Korean relations.

Last month, a White House official said Pence planned to use his attendance to try to counter Kim Jong Un’s efforts to “hijack” the games with a propaganda campaign.

North Korea has agreed with South Korea to send a 230-strong cheering squad to the Winter Olympics, as well as an orchestra and taekwondo performance team.

A joint cultural performance planned in a North Korean mountain resort was called off this week by Pyongyang, which blamed South Korean media for encouraging “insulting” public sentiment regarding the North.

Twenty-two North Korean athletes will compete in the Olympics, including 12 who will play in a unified women’s ice hockey team. The other 10, including a figure skating pair, arrived in South Korea on Thursday.

(Reporting by Christine Kim; Additional reporting by David Brunnstrom, Susan Heavey and Doina Chiacu in Washington; Editing by Simon Cameron-Moore and James Dalgleish)