South Korea is protesting a remark by Japanese Prime Minister Shinzo Abe, who said US forces in Japan cannot be deployed to South Korea for an emergency on the Korean Peninsula unless Tokyo gives approval.
Abe was speaking during Wednesday's Diet deliberations over Japan's ability to exercise its right to collective self-defense.
The Prime Minister said that because US Marines to be sent to the Korean Peninsula are based in Japan, the US would need to talk to Japan before mobilizing them.
South Korea claims such approval is not necessary.
A South Korean military official said deployment would work in accordance with the existing agreement between the US and South Korea.
South Korean media cited a military official as saying US forces would be deployed automatically, so there would be no basis for Japan's intervention.
A report by a Japanese government panel in 2010 concluded that a secret agreement to allow US forces to be deployed without prior discussion is no longer effective.
Then foreign minister Katsuya Okada later revealed he had reaffirmed with the US government the need for prior consultation.
Jul. 17, 2014 - Updated 00:45 UTC