( CNN ) -- U.S. Secretary of State John Kerry and his South Korean and Japanese counterparts warned North Korea against any `` provocative '' moves Sunday ahead of a possible new nuclear bomb test by Pyongyang . Opinion : For South Koreans , a familiar tone from Pyongyang . In a round of calls Sunday , Kerry , Japanese Foreign Minister Fumio Kishida and South Korea 's Kim Sung-hwan all agreed the North must understand `` that it will face significant consequences from the international community if it continues its provocative behavior , '' according to a summary of the calls from the U.S. State Department . Earlier Sunday , North Korea announced that its leader , Kim Jong Un , `` has made an important decision '' that would strengthen the country . The brief statement on the state-run news agency KCNA provided no details , but it said the decision was made at a meeting of the reclusive Stalinist state 's Party Central Military Committee . Across the Demilitarized Zone , South Korean President Lee Myung-bak called on his government to be prepared for a possible test . Lee paid a visit to the underground bunker that serves as the South 's crisis management center , his press office reported . South Koreans cast wary eyes to the North . North Korea has conducted two previous nuclear tests , in 2006 and 2009 , and proclaimed itself a `` nuclear state '' in 2012 . U.S. officials told CNN last week that the North appeared to be ready test another nuclear device `` at any time . '' U.S. analysts believe the 2006 test had a yield of about 1 kiloton -- comparable to the explosive power of about 1,000 tons of TNT -- while the second was roughly 2 kilotons , National Intelligence Director James Clapper told a Senate committee in 2012 . By comparison , the bomb the United States dropped on Hiroshima in 1945 was roughly 15 kilotons . Where North Korea stands in its pursuit of a nuclear missile . The U.N. Security Council voted to tighten sanctions on Pyongyang in January , after the North launched a satellite aboard a long-range rocket in December . The North Koreans responded by announcing they planned another nuclear test and more long-range rocket launches as part of a new phase of confrontation with the United States .
U.S. , South Korea and Japan warn of `` significant consequences '' after a bomb test . " The North Korean government has denied the country carried out any nuclear test. South Korea 's president tells his government to be prepared .