North Korea's nuclear test on Sunday may have produced an explosive yield of 120 kilotons, eight times more powerful than the atomic bomb dropped on Hiroshima in 1945, State Minister of Defence Tomohiro Yamamoto said Tuesday, Japan's Jiji Press reported.

The figure represents an upward revision to the government's initial estimate of 70 kilotons released shortly after the blast.

Yamamoto made the remark in response to a question by Keizo Takemi of the ruling Liberal Democratic Party during a meeting of the Foreign Affairs and Defense Committee of the House of Councillors, the upper chamber of Japan's parliament.

The initial estimate was based on the announcement by the Preparatory Commission for the Comprehensive Nuclear Test Ban Treaty Organisation, or the CTBTO, that the nuclear test caused an artificial earthquake with a magnitude of 5.8 on the open-ended Richter scale.

The CTBTO is closely analysing the seismic waves from the explosion. Some officials said the magnitude may have reached 6.0.

Yamamoto said if the magnitude is put at 6.0, the estimated yield reaches 120 kilotons. The bomb that the United States dropped on Hiroshima in 1945 generated a yield of 15 kilotons.

-- BERNAMA