A flare-up in territorial tensions between Japan and South Korea led to the cancellation of a three-way news conference with the United States on Wednesday, dealing a blow to Washington's hopes of presenting a unified front to the challenge of a nuclear-armed North Korea.

In Tokyo, Chief Cabinet Secretary Hirokazu Matsuno said Japan decided to pull out of the press event, that was to be held after trilateral talks in Washington, due to a recent visit by South Korea's top police official to a pair of Seoul-held, Tokyo-claimed islets in the Sea of Japan.

The event was instead held alone by U.S. Deputy Secretary of State Wendy Sherman.

Sherman explained at the press conference held at the U.S. State Department that one of multiple bilateral "differences" between Tokyo and Seoul, which was "unrelated" to the trilateral meeting, led to the change.

But she added that the vice-ministerial meeting was "very constructive," which "demonstrates exactly why the trilateral format with the United States, Japan and the Republic of Korea is so important and powerful." The Republic of Korea is South Korea's formal name.

File photo shows (From L) South Korean First Vice Foreign Minister Choi Jong Kun, Japan's Vice Foreign Minister Takeo Mori and U.S. Deputy Secretary of State Wendy Sherman pose for a photo in Tokyo on July 21, 2021. (Kyodo)

The incident, however, would likely please North Korea and China. The South Korean police chief's visit Tuesday to the islets, known as Takeshima in Japan and Dokdo in South Korea, was reportedly the first from someone in the position in more than a decade and drew strong protest from Japan.

The State Department had been planning a joint press conference involving Sherman, Japanese Vice Foreign Minister Takeo Mori and South Korea's First Vice Foreign Minister Choi Jong Kun after their meeting, which lasted for more than three hours.

U.S. President Joe Biden's administration has been striving to promote cooperation between Japan and South Korea, viewing trilateral relations -- despite the wartime history and territorial disputes between two of its allies in Asia -- as vital in the face of North Korean nuclear threats and China's assertiveness in the region.

The gathering on Wednesday was the first trilateral vice-foreign ministerial-level meeting since Japanese Prime Minister Fumio Kishida took office in October. The joint press conference was apparently a chance to showcase enhanced ties.

Japanese Foreign Ministry sources said the Takeshima issue was not discussed during the trilateral meeting. But the government decided that it was "not appropriate" to hold a joint press conference when Tokyo is protesting to South Korea over the matter.

U.S. Deputy Secretary of State Wendy Sherman holds a press conference at the State Department in Washington on Nov. 17, 2021. (Kyodo) 

According to a press release issued by the U.S. State Department, the three officials reaffirmed that trilateral cooperation "is essential to tackling the most pressing challenges" in the region and across the globe, while sharing a commitment to maintaining a rules-based international order.

They also discussed the importance of the peace and stability of the Taiwan Strait, while sharing concerns over North Korea's nuclear and missile programs and an intention to closely cooperate toward the complete denuclearization of the Korean Peninsula.

The deputy secretary of state said the United States will continue discussions to explore the best way forward to ensure Pyongyang's denuclearization, with South Korea proposing the declaration of a formal end to the Korean War as part of confidence-building measures with North Korea.

"On (the issue of the) end of war...we are having good consultations amongst us and with other allies and partners and we will continue to do so," Sherman said.

The United States and North Korea remain technically in a state of war as the 1950-1953 Korean War -- in which U.S.-led U.N. forces fought alongside the South against the North, backed by China and the Soviet Union -- ended in a cease-fire, not a peace treaty.

North Korea has called for the United States to abandon its "hostile policies." A security guarantee is seen as a prerequisite for North Korea to give up its nuclear arms.

But diplomatic sources have previously said that Tokyo is reluctant to support the idea, believing it would only create a conciliatory mood without clear prospects that Pyongyang would abandon its nuclear weapons and resolve the issue of its past abductions of Japanese nationals.

One of the two Japanese Foreign Ministry sources who briefed on Wednesday's trilateral meeting acknowledged discussions regarding the declaration are under way based on "respective positions" on the issue, but did not elaborate.

After the trilateral talks, Mori and Choi had a bilateral meeting, during which they sparred over the Takeshima issue.

Mori said the South Korean police chief's visit to Takeshima was "unacceptable," given that the islands are "an inherent part of the territory of Japan, in light of historical facts and based on international law," according to the other Foreign Ministry source.

Mori also expressed his awareness that the bilateral ties remain in a "very difficult" state due to disputes stemming from Japan's colonial rule of the Korean Peninsula between 1910 and 1945, such as compensation over forced labor and the "comfort women" issue.

But the two agreed to continue communication through their diplomats to put relations back on a sound footing, according to the Japanese Foreign Ministry's press release.

Speaking at a press briefing in Seoul on Thursday, Foreign Ministry spokesman Choi Young Sam repeated South Korea's position on the disputed islets.

"Dokdo is clearly our inherent territory," Choi said. "We will firmly respond to Japan's unreasonable claims over the islets."

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