The escalation in the war of words comes after President Donald Trump tweeted Kim Jong Un "won't be around much longer."
Several North Korean missiles were recently spotted moved from a rocket facility in the capital Pyongyang, South Korea's Korean Broadcasting System (KBS) reported late on Friday.
The report cited an unnamed intelligence source saying South Korean and US intelligence detected missiles being transported away from North Korea's Missile Research and Development Facility at Sanum-dong in the northern part of Pyongyang.
The report did not say when or where they had been moved, reports News.com.au.
The missiles could be either intermediate range Hwasong-12 or intercontinental ballistic Hwasong-14 missiles, according to the report, though the missile facility at Sanum-dong has been dedicated to the production of intercontinental ballistic missiles.
South Korean officials have voiced concerns that North Korea could conduct more provocative acts near the anniversary of the founding of its communist party on October 10, or possibly when China holds its Communist Party Congress on October 18.
The US President said the use of force is not Washington's first option, but they will do what it takes to stop Kim Jong-un.
A man watches a TV screen showing a file footage of North Korea's missile launch, at the Seoul Railway Station in Seoul, South Korea, Tuesday, Aug. 29, 2017. Photo / AP
"We are totally prepared for the second option, not a preferred option," he said, referring to military force.
"But if we take that option, it will be devastating, I can tell you that, devastating for North Korea. That's called the military option. If we have to take it, we will."
It comes as US officials said satellite imagery also detected North Korean military assets relocating to the country's east coast.
Tensions on the Korean peninsula have increased markedly since North Korea's sixth nuclear test on September 3, which led to a new round of sanctions against the North after a unanimous UN Security Council resolution.
"(The) yield is much bigger than the previous test, and it means North Korea made very rapid progress," International Atomic Energy Agency (IAEA) Director Yukiya Amano told reporters in Seoul on Friday.
"Combined with other elements, this is a new threat and this is a global threat," he said after a meeting with South Korean Foreign Minister Kang Kyung- wha.
Amano said the IAEA did not have the capacity to determine whether the North had tested a hydrogen bomb, as Pyongyang has claimed.
"What is most important for now is for the international community to unite," Amano said.
Tensions had already flared after North Korea tested two more intercontinental ballistic missiles and other launches as it pursues its nuclear and missile programs in defiance of international pressure.
South Korea said on Thursday the North could engage in more provocations near the anniversary of the founding of the North Korean communist party and China's all-important Communist Party Congress.
