SEOUL (AFP/Reuters) - North Korea on Monday tested a nuclear bomb many times more powerful than its first in 2006, angering enemies and allies alike and prompting UN Security Council members to call an emergency session. Ratcheting up tensions further, North Korea test-fired three short-range missiles just hours later, Yonhap news agency said. The hardline communist state, which stunned the world with its first atomic bomb test in October 2006, made good on its threat to stage another test after the Security Council censured it for an April rocket launch. The North successfully conducted one more underground nuclear test on May 25 as part of the measures to bolster up its nuclear deterrent for self-defence in every way, the official Korean Central News Agency (KCNA) said. The current nuclear test was safely conducted on a new higher level in terms of its explosive power and technology, it said. The force of Mondays blast was between 10 and 20 kilotons, according to Russias defence ministry, vastly more than the estimated one-kiloton blast three years ago. Japans Meteorological Agency said that based on recorded seismic activity, the energy level of the test was four times bigger than the last one. Baek Seung-Joo of the Korea Institute for Defence Analyses told AFP that if rough estimates by some private analysts are right, the power of the second blast is comparable to the bombs which hit Hiroshima and Nagasaki. The Security Council, which sanctioned the North for its previous test, planned to meet Monday afternoon in New York. The North also test-fired three short-range missiles Monday, South Koreas military said. The North informed the United States and China in advance of the test, a South Korean official said on condition of anonymity. Japans Foreign Minister Hirofumi Nakasone said that his country, as the only atomic-bombed nation, needed to take stern action. Japan asked UN Security Council chair Russia to call an emergency meeting. The KCNA report did not say where the nuclear test was conducted. South Korean officials said a tremor was detected around the northeastern town of Kilju, near where the first test was staged. A nuclear test carried out by North Korea on Monday is slightly bigger than the one carried out by Pyongyang in 2006, the Vienna-based nuclear test ban treaty organisation said, contesting reports of a bigger blast. Russias Itar-Tass agency quoted a source in Russias defence ministry as saying the test had a force of about 20 kilotonnes, compared with a generally accepted strength of about one kilotonne in 2006. A kilotonne is equivalent to 1,000 tonnes of TNT. The events magnitude is slightly higher than in 2006, measuring 4.52 on the Richter scale, while in 2006 it was 4.1, the Comprehensive Nuclear-Test-Ban Treaty Organisation (CTBTO) said in a statement. The tremor took place just below the ground, within a couple of kilometres from the previous test and has an estimated low single digit kiloton range, the CTBTO said.