"The only winners when Japan and Korea feud are our competitors", Schriver told the Centre for Strategic and International Studies. "We only have to look at the recent patrol by Russian and Chinese aircraft as a direct challenge to our three countries and an attempt to take advantage of the current frictions".
The United States fears the end of intelligence sharing reflects "serious misapprehension" by the administration of South Korean President Moon Jae-in regarding security challenges in Northeast Asia from China, Russia and North Korea, Schriver said.
"Historical disputes animosities and political disagreements [between South Korea and Japan] should be kept separate from shared vital military and security cooperation", Schriver said.
In a tense confrontation last month involving aircraft from South Korea, Japan, Russia and China, Seoul claimed to have fired warning shots at a Russian military aircraft over the Sea of Japan - an account that was disputed by Moscow.
Japan backed up South Korea's claims, saying Tokyo had sent fighter jets to intercept the Russian aircraft and that two Chinese bombers had joined the Russian airplanes.
The feud began with South Korea demanding payments from former colonial ruler Japan in a dispute that predates World War II. The standoff escalated into a trade war followed by South Korea’s decision to scrap a 2016 agreement to share military intelligence with Japan without the United States as a go-between.