TOKYO — A group of 58 retired American military leaders is making a rare public plea to President Trump, urging him not to take military action against North Korea and instead to pursue a diplomatic resolution to the current standoff.

As North Korea has demonstrated its increasing technical abilities, including the capacity to send a missile anywhere in the United States, Trump and some of his top aides have suggested that a military strike on North Korea might be the solution.

North Korean leader Kim Jong Un vowed to “win victory in the showdown” with the United States, state media reported Wednesday.

Dozens of retired military leaders from across the services are writing to Trump to urge him not to start a conflict with North Korea, and instead to choose diplomacy.

“The current approach taken by the United States is failing to stop North Korea from developing its nuclear and missile technology,” states the letter, which will be sent to the White House on Wednesday. “The United States must initiate and lead an aggressive, urgent diplomatic effort to freeze North Korean nuclear and missile development and reduce regional tensions.”

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The. U.S., South Korea and Japan held a joint-missile tracking drill on Dec. 11 as tensions rose on the Korean Peninsula over North Korea's fast-developing weapons program. (Reuters)

Military action would result in hundreds of thousands of casualties in South Korea, putting the lives of more than 150,000 Americans there at risk, and the United States would be drawn into a preventable war, the letter says.

“Military options must not be the preferred course of action,” it continues. (Full text below.)

The 58 retired admirals and generals who signed the letter were motivated by the deteriorating situation in North Korea, said Michael E. Smith, a retired Navy rear admiral who initiated the letter and leads a new nonpartisan organization called the American College of National Security Leaders.

“We felt we had a moral obligation to share our concerns with the president,” Smith said. “It is clear that more can be done and we are urging the president to explore every possible diplomatic option before it is too late and we find ourselves in a dangerous and preventable war."

The fact that former military leaders were prepared to come out publicly on such a sensitive issue shows how strongly they feel about it, said Tom Z. Collina, director of policy at the Ploughshares Fund, a nonprofit organization that advocates for nuclear disarmament.

Ploughshares is working with the American College of National Security Leaders to promote a diplomatic solution to the crisis in North Korea.

“It is very difficult to get senior officers to speak out on an issue like this where troops could soon be sent into action,” Collina said. “This is very sensitive.”

The Trump administration is continuing to send mixed signals to North Korea.

Right now is the “last, best chance to avoid conflict” with North Korea, but “time is running out,” H.R. McMaster, Trump’s national security adviser, said at a British think tank Tuesday.

But even as McMaster was speaking in London, Secretary of State Rex Tillerson said that the Trump administration wants talks.

“We’ve said from the diplomatic side we’re ready to talk anytime North Korea would like to talk, and we’re ready to have the first meeting without precondition,” Tillerson told a forum at the Atlantic Council in Washington on Tuesday.

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At the 2017 Atlantic Council-Korea Foundation Forum on Dec. 12, Secretary of State Rex Tillerson said the U.S. is ready to talk with North Korea with no preconditions on the first meeting. (Reuters)

Joseph Yun, the State Department's envoy on North Korea policy, is in Tokyo and Bangkok this week for talks with government officials about “ways to strengthen the pressure campaign” against North Korea after its latest ballistic missile test, the State Department said.

North Korean officials are struggling to decipher the Trump administration’s policy and the president’s tweets. They have contacted former officials, some with Republican ties and some who have been involved in North Korea policy in the past, to ask them to interpret Trump for them.

Below is the full text of the letter:

Dear Mr. President: