Renewed calls in South Korea for the redeployment of U.S. tactical nuclear weapons to the country or its own nuclear armament reflect concerns that U.S. security guarantees are "fragile," a U.S. congressional report said.

The North's fourth nuclear test in January and its long-range rocket launch in February have led some leading members of South Korea's ruling party to make the case for nuclear armament, arguing that it makes no sense to rely on the U.S. "nuclear umbrella" as the North's nuclear arsenal grows.

But the government rejected the idea as contrary to the principle of a nuclear-free Korean Peninsula.

"Some politicians in South Korea have called for the return of U.S.  nuclear weapons to the peninsula, or even South Korea's development of its own nuclear capability, as a response to North Korea's development and testing of nuclear weapons," the Congressional Research Service said in a report on nonstrategic nuclear weapons.

"This view has not received the support of the current government in South Korea, but it does demonstrate that some may see U.S. security guarantees as fragile," it said.

The report also said that the debate over the relationship between U.S. nuclear weapons and nonproliferation policy has also focused on extended deterrence and the assurances the United States provides to its allies. Many analysts have argued that, if these allies were not confident in the reliability and credibility of the U.S. nuclear arsenal, they may feel compelled to acquire their own nuclear weapons, it said.

Such a view is evident among analysts who express concerns that Turkey, in particular, with its proximity to Iran, might pursue its own nuclear weapons if the United States were to withdraw its tactical nuclear weapons from Europe, the report said.

"Such calculations might also be evident in Japan and South Korea, as they face threats or intimidation from nuclear-armed neighbors like China and North Korea," it said.

Calls for South Korea's nuclear armament were fueled by U.S. Republican presidential front-runner Donald Trump's suggestion that he could allow the Asian ally to develop its own nuclear arsenal for self-defense in order to reduce U.S. security burdens.

But the suggestion has since been strongly denounced as contrary to nonproliferation principles.

U.S. President Barack Obama has also openly criticized Trump, saying the statements about nuclear armament "tell us that the person who made the statements doesn't know much about foreign policy or nuclear policy or the Korean Peninsula or the world generally."

Secretary of State John Kerry also slammed the suggestion, saying nothing can be "more volatile" or "more contrary" to peace and stability. (Yonhap)