South Korea’s chief nuclear envoy, Kim Gunn, and his US counterpart, Sung Kim, will meet in Washington on Monday to review joint work on disarming North Korea, the Foreign Ministry in Seoul said in a statement Friday, amid heightened inter-Korean tensions.

Last week, Pyongyang failed to put into orbit what it claimed was a military reconnaissance satellite, a launch that some believe was actually meant to test a ballistic missile. United Nations Security Council resolutions ban the isolated country from testing any such technology.

Both Seoul and Washington, its biggest ally, have openly warned of stern responses should Pyongyang repeat such launches. Defying international sanctions, the North says it will exercise its right to self-defense as it prepares for a second test.

Meanwhile, experts said the same day that the South should deepen security ties with not only the US but also Japan in order to deal with an increasingly aggressive North Korea. Seoul, Washington and Tokyo are part of a three-way coalition working on the North’s disarmament.

At a forum held in Seoul to mark President Yoon’s first anniversary of taking office in May, Ko Jae-hong, deputy director at the Institute for National Security Strategy, said closer Seoul-Tokyo ties are important because the “two neighbors without nuclear weapons could mutually benefit from each other by setting a united front on Pyongyang.”

Yang Uk, a research fellow at the Asan Institute for Policy Studies, said South Korea should factor into tighter China-Russia ties because those two permanent members with veto power on the UNSC will continue to thwart any attempts to sanction North Korea.

“Not only that, the Yoon administration should be aware of potentially waning US support for a hard line on North Korea. The issue has been going on without resolutions for years. Some are getting tired of it,” Yang noted.