For the US, which nurtures military alliances with both countries, the standoff poses a foreign policy dilemma that worsened this month when Korea's President Lee Myung-bak, seeking to improve sagging popularity ratings, visited Dokdo and called on Japan's Emperor Akihito to apologize for all the wrongs of Japanese colonialism.
"It's a very delicate problem for the US," says David Straub at the Korean Studies Center at Stanford University. "They are both allies and friends, but the US doesn't have influence."
The dispute has broader military implications that distract from common defenses against North Korea. Although Japan and South Korea are not threatening to go to war over the issue, South Korea stages military exercises around the islands that are clearly directed against Japan.
"From an American point of view, it's an embarrassment," says Mr. Straub, a former senior US diplomat here. Other than stressing the need for both sides to get along with one another, he says, "there's nothing that can be done."