It was the first time that Seoul suggested a willingness to provide weapons to Ukraine, more than a year after ruling out the possibility of lethal aid.
During the summit, Yoon said he will seek "tangible outcomes" on the allies' efforts to improve responses to evolving threats from North Korea, which has ramped up military tests, and launched its first solid-fuel intercontinental ballistic missile last week.
In February, South Korea and the U.S. staged table-top exercises simulating a North Korea nuclear attack as part of Seoul's efforts to play a bigger role in Washington's nuclear policy over the North.
"I think there's no big problem if Japan is joining, but since there's been much progress between the U.S. and South Korea, it would be more efficient to create this system ourselves first."
"The Taiwan issue is not simply an issue between China and Taiwan but, like the issue of North Korea, it is a global issue."