Hong Kong After Pyongyang confirmed it had gone ahead with the test in defiance of international pressure, world leaders responded with condemnation. "This is a highly provocative act" that threatens regional stability, breaches U.N. resolutions and increases the risk of proliferation, U.S. President Barack Obama said in a statement. "North Korea's nuclear weapons and ballistic missile programs constitute a threat to U.S. national security and to international peace and security," he said. "It is a clear and grave violation of the relevant Security Council resolutions," the office of Ban Ki-moon, the secretary-general of the United Nations, said in a statement referring to the test. The United Nations Security Council will meet in New York on Tuesday morning to discuss the development, a security council diplomat said. Japanese Prime Minister Shinzo Abe said the test was "extremely regrettable," adding that Tokyo would "strongly" protest it. Kim Min-seok, a spokesman for the South Korean defense ministry, said the magnitude of the "artificial tremor" suggested the size of the blast could be in the order of 6 to 7 kilotons, more powerful than the North's two prior nuclear tests. --SPA 11:27 LOCAL TIME 08:27 GMT www.spa.gov.sa/1077652