When it comes to Japan, the United States and the Republic of Korea are in the same bed but with different dreams, as the Chinese saying would have it.

Their differences on Japan manifested themselves at a news conference jointly held by US Secretary of State John Kerry and his South Korean counterpart, Yun Byung-se, in Seoul in mid-February.

Kerry came to Seoul as part of an Asian tour that also took him to Beijing, Jakarta and Abu Dhabi.