South Korea says North's nuclear capability 'speeding up,' calls for action

South Korea's foreign minister said on Saturday thatNorth Korea's nuclear capability has reached a "considerable level,"echoing the alarm aired around the world over the isolated state's fifth nuclear test brazenly defying 10 years of UNsanctions.

North Korea conducted its fifth and biggest nuclear test on Friday and said it had mastered the ability to mount a warhead on a ballistic missile, ratcheting up a threat that rivals and the United Nations have been powerless to contain.

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The blast, on the 68th anniversary of North Korea's founding, drew a fresh wave of global condemnation. The United States said it would work with partners to impose new sanctions, and called on China to use its influence as North Korea's main allyto pressure Pyongyang to end its nuclear program.

"North Korea's nuclear capability is growing and speeding to a considerable level, considering the fifth nuclear test was the strongest in scale and the interval has quickened substantially,"South Korean Foreign Minister Yun Byung-se said at a meeting in Seoul.

Yun added that the test proved North Korean leader Kim Jong-unwas clearly unwilling to change and tougher sanctions and pressure were needed to apply "unbearable pain on the North to leave no choice but to change."

Under the 32-year-old third-generation leader Kim, North Korea has sped up development of its nuclear and missile programmes, despite U.N. sanctions that were tightened in March and have further isolated the impoverished country.

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The United Nations Security Council denounced North Korea's decision to carry out the test and said it would begin work immediately on a resolution. The United States, Britain and France pushed for the 15-member body to impose new sanctions.

South Korean newspapers sounded the alarm on Saturdayover what one termed the "nuclear maniac"Kim Jong-un, saying the North Korean leader's fifth and biggest nuclear test is a game-changer demanding a tougher response.

South Koreanactivists, meanwhile,gathered in Seoul where theyset fire to a portrait of Kim ina protest denouncing thenuclear test.