The president said stronger ties with South Korea and Japan are working, but did not address whether President-elect Donald J. Trump would continue his approach when he takes office in January.

The recently signed mutual defense treaty could be used to justify thewidening of the war in Ukraine, as the U.S. says North Korean and Russian troops are already battling Ukrainian forces.

US President Joe Biden told the leaders of Japan and South Korea that their coordinated efforts were essential to “countering North Korea’s dangerous and destabilizing cooperation with Russia” as they met Friday on the sidelines of the APEC Summit in Lima.