The visit by the envoy, Morgan Ortagus, coincided with a spike in Israeli attacks on Hezbollah in recent weeks that has stoked fears of a renewed conflict.
President Trump lamented not being able to speak with Mr. Kim, the North Korean leader, but vowed to end the decades of hostilities between the two Koreas.
It needs the United States for defense and has spent billions building factories in America. But a Trump trade deal this week with China could erase a Korean edge in the U.S. market.