North Korea has moved a missile with "considerable range" to its east coast, South Korea's defence minister has said.
Minister Kim Kwan-jin said he did not know the reasons behind the missile movement, saying it "could be for testing or drills".
However, he added that it is not capable of hitting the United States.
Minister Kwan-jin said there are no signs that North Korea is preparing for a full-scale conflict.
The report came hours after North Korea's military warned that it has been authorised to attack the US using "smaller, lighter and diversified" nuclear weapons.
It was the North's latest war cry against the US in recent weeks, with the added suggestion that it had improved its nuclear technology.
The Pentagon in the US said it will deploy a high-altitude missile defence system to Guam.
The deployment is to strengthen the Asia-Pacific region's protections against a possible North Korean attack.
The US has already sent bombers, stealth fighters and ships to the region.
Experts say North Korea has not demonstrated that it has missiles capable of long range or accuracy.
Some suspect that long-range missiles unveiled by Pyongyang at a parade last year were actually mock-ups.
North Korea has been railing against joint US-South Korean military exercises that are taking place in South Korea.
It has expressed anger over tightened UN sanctions for its February nuclear test.
Mr Kim said he believed the North's recent threats were rhetorical.
But he said there is still the possibility of North Korea mounting a localised, small-scale provocation against South Korea.
He cited the 2010 shelling of a South Korean island, an attack that killed four people, as a possible example of such a provocation.
Elsewhere, North Korean border authorities denied entry to South Koreans who manage jointly run factories in the North Korean city of Kaesong, for a second day.
Trucks carrying cargo and South Korean workers were turned back yesterday and again today.