WASHINGTON, May 25 (UPI) -- North Korea's claim to have conducted a successful nuclear test cannot be immediately verified, experts said Monday.
The dimensions of the blast were impossible to confirm, but seismologists said it set off an earth tremor measured at between magnitudes 4.5 and 5.3 on the Richter earthquake scale, The New York Times reported.
Pyongyang's claims of success in its first nuclear test in 2006 were later determined by Washington and Seoul to have been exaggerated, the newspaper said. Monday's tremor emanated from Kilju in northeastern North Korea, the same place as the 2006 test, the seismologists said.
South Korean expert Kim Sung-han told the Times he estimated the test was in the one-kiloton explosive range, a bit more than the 0.8 kiloton 2006 blast, making it a fraction of the size of the bombs that destroyed the Japanese cities of Hiroshima and Nagasaki in 1945.
But Russian Defense Ministry spokesman Alexander Drobyshevsky told RIA Novosti he believed the size of the blast was 10 to 20 kilotons.
North Korea claimed it had "successfully" conducted the nuclear test to "bolster its nuclear deterrent for self-defense."
South Korea's Yonhap news agency reported the testing comes in the wake of the Communist country's warning last month about its nuclear plans in protest of the U.N. Security Council's condemnation of its April 5 long-range rocket launch.
"The Democratic People's Republic of Korea (North Korea) successfully conducted one more underground nuclear test on May 25 as part of measures to bolster its nuclear deterrent for self-defense," the North's official Korean Central News Agency was quoted as saying.
KCNA said the test was of a higher level "in terms of its explosive power and technology of its control."
South Korean President Lee Myung-bak summoned an emergency meeting of security ministers, Yonhap said, adding the Defense Ministry had launched a "crisis management" team of general-level officers.