South Korea, the United States and Japan established a trilateral communication hotline, a senior Seoul official said Monday, in another sign of progress in their three-way security cooperation amid North Korea's evolving military threats and China's increasing assertiveness.

The establishment of the hotline came after President Yoon Suk Yeol and his US and Japanese counterparts, Joe Biden and Fumio Kishida, respectively, agreed on the "commitment to consult" each other in the event of a common threat during their landmark summit at Camp David on the outskirts of Washington in August.

The hotline is said to link the three countries' National Security Councils, enabling voice and video communication among their leaders and top security officials at any time.

"A hotline among the three nations has been established, and a test among (the countries') technicians has also been completed," the official told Yonhap News Agency over the phone, requesting anonymity.

The installation coincided with emerging concerns among experts and policymakers that Pyongyang and Beijing could engage in provocative acts, while Washington is heavily consumed with dealing with the escalating Israel-Hamas war and Russia's protracted war in Ukraine.

In response to a question from Yonhap News on Wednesday last week, a US National Security Council spokesperson said that efforts were under way to improve trilateral communication capabilities to ensure "regular, timely and redundant access to secure lines of voice and video communication."

"The efforts announced as part of the Camp David trilateral summit build upon existing communication capabilities between our three countries," the spokesperson said.

"In addition to facilitating leader-level communications, we are also working to ensure secure connectivity between other senior members of government, including our respective national security advisers," the official added.

Prior to the Camp David summit, White House Indo-Pacific Coordinator Kurt Campbell told a think tank session that Seoul, Washington and Tokyo were going to invest in technology for the hotline as part of efforts to enhance cooperation among the countries' senior officials to prepare for any contingency.

The hotline project came as Pyongyang has been doubling down on its nuclear and missile programs under an aggressive nuclear policy, which was stipulated in its constitution.

Three-way security cooperation gained traction as relations between Seoul and Tokyo took a turn for the better following the Yoon administration's decision in March to address the issue of compensating Korean victims of Japan's wartime forced labor -- long a thorn in the bilateral relations.

The Camp David summit, the three countries' first stand-alone summit, marked the culmination of their cooperation efforts as it produced a set of key agreements, including holding three-way talks among the leaders, foreign ministers, defense ministers and national security advisers at least annually. (Yonhap)