File photo: U.S. Secretary of State Antony Blinken attends a joint news conference at the U.S. Department of State on June 16, 2023 in Washington, DC. AFP
The conversations also come as North Korea has stepped up missile launches in the past year, and Tokyo is also contending with growing pressure from Chinese vessels around islands contested with Beijing.
Blinken reassured Foreign Minister Park Jin of the United States' "ironclad commitment" to South Korea's defense, State Department spokesman Matthew Miller said in a statement.
"The Secretary and the Foreign Minister condemned the DPRK's continued unlawful ballistic missile launches and noted the need for the PRC to use its influence to encourage Pyongyang to engage in serious and sustained diplomacy," he added, using acronyms for North Korea and China's official names.
Blinken repeated the "ironclad commitment" to defense to Japan's Minister for Foreign Affairs Hayashi Yoshimasa, and "condemned the DPRK's continued unlawful ballistic missile launches into the Sea of Japan."
The three countries issued a joint statement Thursday to "condemn" North Korea's launch of two short-range ballistic missiles, shortly after Pyongyang warned of an "inevitable" response to ongoing US-South Korea joint military drills.
Last year, Tokyo unveiled a major defense overhaul, pledging to boost security spending to two percent of GDP by 2027 and calling China the "greatest strategic challenge ever" for Japan.
The trilateral statement reflected the growing thaw between Japan and South Korea -- a major foreign policy goal of President Joe Biden's administration amid tensions in the region and China's growing influence.
Blinken also Saturday told Park, though not Hayashi, of the US pledge to "responsibly manage the US-PRC relationship."
Blinken will visit China on Sunday and Monday in the first trip by a top US diplomat in nearly five years.
The visit was rescheduled after a planned trip to Beijing in February was canceled when Washington said it detected -- and later shot down -- a Chinese spy balloon.
US President Joe Biden told reporters Saturday morning that he also hoped to meet with his Chinese counterpart Xi Jinping "over the next several months" to talk about "legitimate differences we have but also how... to get along."