North Korea test-fired the medium-range Musudan - capable of hitting US bases as far away as Guam - on Saturday.

"Musadan could probably hit Guam, but the next larger rocket would probably be able to hit the USA", she said.

South Korea's Yonhap news agency said "extended deterrence" could include permanent deployment of U.S.

"Make no mistake, any attack on America or our allies will not only be defeated, but any use of nuclear weapons will be met with an overwhelming and effective response", he added.

Carter said the USA and South Korea would "continue to modernize our alliance, seize new opportunities and address evolving threats".

"The U.S. has nuclear weapons off our coast, targeting our country, our capital and our dear leader, Kim Jong Un", Lee said. "The next few years will be the tipping point". "THAAD, once deployed, would complement Patriot by providing an upper tier defense", Heinrichs said.

As part of the military effort, Kerry said the United States would deploy the Terminal High Altitude Area Defense anti-missile system to South Korea "as soon as possible".

Kerry called for every country to rigorously enforce United Nations sanctions on North Korea, which are intended - but have failed - to prevent its development of weapons of mass destruction.

"If the North continues to violate worldwide law by pursuing its ballistic missile and nuclear weapons programs, it will come under even stiffer sanctions, greater pressure and be left further and further behind while the rest of the region prospers", he said.

After Pyongyang carried out its fourth nuclear test in January, the Security Council adopted the toughest sanctions resolution to date, targeting North Korea's trade in minerals and tightening banking restrictions.

The Musudan has a range of some 3,000 kilometers, posing a threat to South Korea and Japan, and possibly the US territory of Guam.

The MTCR should close the loopholes in their export control regime in order to block out the inflow of sensitive missile components to North Korea, Lim underlined. Kerry said that provision was being abused and the "greatest amount" of coal and revenue has just passed between China and North Korea.

"We do not, and we will not, accept North Korea as a nuclear-armed state", he said.

Permanent deployment of such military hardware is expected to reassure South Koreans of the USA defense commitment amid heightened security jitters that sparked calls for developing the country's own nuclear weapons or bringing US nuclear bombs back into the country. "Our warning is not an empty word".

Kerry said claims from North Korean leader Kim Jong Un that he needs nuclear weapons to defend against the USA defy common sense.

Earlier this month, the White House rejected a petition against the move, signed by more than 100,000 people, saying that the THAAD was a means to "improve the missile defense posture of the US-[South Korea] alliance" against "North Korea's continued provocations and refusal to engage in serious negotiations on denuclearization".

The Pentagon is also devoting resources to new capabilities critical to the rebalance, he said, adding that the United States is increasing the number of surface ships and making each of them more lethal, while investing in Virginia-class submarines, advanced undersea drones, the new B-21 long-range strike bomber, and state-of-the-art tools for cyberspace, electronic warfare, and space.