Washington needs the support of South Korea, China and Japan for sanctions to be effective because the trio all have economic links with North Korea.

South Korea's foreign ministry said on Friday it was "not time" for sanctions, arguing that diplomacy had not run its course.

Western diplomats said it was too early to tell whether there had been a policy shift in Seoul.

Mr Roh's visit to the US appeared to be narrowed differences between Seoul and Washington about policy towards North Korea.