US Secretary of State Antony Blinken and South Korean, Japanese counterparts expressed "serious concern" over the discussion of military cooperation between Russia and North Korea, including possible arms trade, South Korea's Foreign Ministry said on Saturday.
Blinken, South Korea's Foreign Minister Park Jin and Japan's Foreign Minister Yoko Kamikawa agreed to respond firmly to any acts that threaten regional security in violation of UN Security Council resolution in a brief meeting on Friday, the ministry said in a statement.
North Korea's leader Kim Jong Un made a weeklong visit to Russia last week and discussed military cooperation with Russian President Vladimir Putin.
US and South Korean officials have expressed concern that the summit was aimed at allowing Russia to acquire ammunition from the North to supplement its dwindling stocks for its war in Ukraine.
South Korean President Yoon Suk Yeol said on Wednesday that if Russia helped North Korea enhance its weapons programs in return for assistance for its war in Ukraine, it would be "a direct provocation" and Seoul and its allies would not stand idly by.