South Korea on Thursday warned North Korea of \"grave consequences\" and new international sanctions if the North goes ahead with a nuclear test, Yonhap News Agency reported. \"If North Korea goes ahead with a nuclear test, it will be a clear breach of the April 19 presidential statement by the UN Security Council and therefore the Security Council will have to take new actions,\" Foreign Ministry spokesman Cho Byung-jae said in Seoul, according to the report. \"Should North Korea go ahead with a nuclear test, it will bring about grave consequences that do not help North Korea at all,\" Cho was quoted as saying. Officials and analysts believe that the North may soon set off a nuclear device following its failed launch of a long-range rocket on April 13. Pyongyang\'s two previous rocket launches in 2006 and 2009 were followed by nuclear tests. The UN Security Council tightened sanctions against North Korea over the failed launch, strongly condemning it as a violation of UN resolutions that ban the North from testing ballistic missile technology and warning of additional actions if Pyongyang conducts another missile or nuclear test. Also on Thursday, Defense Ministry spokesman Kim Min-seok said the North\'s nuclear test is just a matter of time and Pyongyang is waiting to make a political choice. \"Our judgment is that North Korea can conduct a nuclear test at any time and a political choice is left\" before testing, Kim said. South Korea, the US and Japan have pressed North Korea to back down on a nuclear test, but the North vowed to boost its nuclear deterrent as long as the US sticks to what it calls a \"hostile policy\" against the communist regime.