Secretary of State John Kerry was in South Korea Friday as the North Koreans reportedly put more missiles into launch position.
Five are now said to be ready.
Earlier reports indicated that they may be armed with nuclear warheads.
Secretary Kerry now says that is probably not the case.
"They have conducted a nuclear test so there is some kind of device. But that is very different from miniaturization and delivery," Secretary Kerry said.
Kerry made it clear that North Korean leader Kim Jong Un must not build more nukes or launch any missiles.
"It is a huge mistake for him to chose to do that, because it will further isolate his country," Kerry warned.
What might jar North Korea into backing off?
China could pull the plug on food aid, meaning more North Koreans could starve.
That would be a disaster for Kim's government.
Kerry goes next to Beijing to try to get China to take a tougher stance.