North Korea test seen "slightly bigger" than in 2006

By Sylvia Westall

VIENNA (Reuters) - A nuclear test claimed 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, contradicting reports of a bigger blast.

Russia's Itar-Tass agency quoted a source in Russia's 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 event's 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" kilotonne range, the CTBTO said.

"This is the wrong step in the wrong direction," CTBTO Executive Secretary Tibor Toth told reporters.

The CTBTO, the world's independent body for monitoring possible breaches of the test ban, has collected data from 39 seismic stations around the world and is awaiting detail on possible radioactive particles and noble gases.

New stations close to the DPRK, in China, Japan and Russia had helped speed up readings and make them more precise, the CTBTO said.