BANGKOK — U.S. Defense Secretary Mark Esper said Sunday the United States and South Korea have indefinitely postponed a joint military exercise in an “act of goodwill” toward North Korea.

The move comes even as Japan’s defense minister, whose country feels threatened by repeated North Korean missile launches, told Esper “no one could be optimistic about” changing the North’s behavior.

The statement by Japan’s defense chief, Taro Kono, was a stark illustration of the difficulties facing the U.S. and its international allies and partners as they struggle to get North Korea back to negotiations to eliminate its nuclear weapons and missiles. Talks launched by President Donald Trump in 2018 have stalled with no resumption in sight.

Although the U.S. military for years as called its joint military exercises with South Korea an important means of keeping troops and commanders ready for combat on short notice, Trump has called them a waste of money and a provocation to the North.

The U.S. has about 28,000 troops in South Korea.

Esper announced the postponement of the military exercise at a joint news conference with his South Korean counterpart, Jeong Kyeong-doo.

Esper insisted the postponement was not a concession to North Korea but rather an attempt to “keep the door open” to diplomacy to eliminate North Korea’s nuclear weapons.

“I see this as a good-faith effort by the United States and the Republic of Korea to enable peace; to shape to, facilitate a political agreement that leads to the denuclearization of the Korean Peninsula,” Esper said.

In response, the North Korean Foreign Ministry issued a written statement of defiance. It said it has no plans to negotiate over its nuclear programs, even if talks were to resume, unless the U.S. offers to first discuss the withdrawal of its “hostile” policies against Pyongyang.

North Korea also criticized Washington’s support of a recent United Nations resolution condemning the North’s widespread human rights violations, claiming that the resolution shows continued U.S. intent to isolate the North and destroy its political system.

The North also has harshly criticized U.S.-South Korean military drills as provocative and as preparations for an invasion.

Kono met with Esper and Jeong after their announcement. Kono said it was important that the three nations consult closely “under the current situation where no one could be optimistic about North Korea.”

He added that the North Koreans have launched “more than 20 missiles this year including new types of missiles as well as a submarine-launched ballistic missile” in violation of U.N. Security Council resolutions.

Esper said he did not consider the postponement a concession to North Korea, although it follows earlier cutbacks in the scale of such exercises.

“We have made this decision as an act of goodwill to contribute to an environment conducive to diplomacy and the advancement of peace,” Esper said.