Heightened activity at a North Korean nuclear test site could be a bluff rather than preparations to set off an atomic device soon, the head of an international body set up to monitor a ban on nuclear testing said on 7 December in Seoul, South Korea.

A report by 38 North, a North Korea project at Johns Hopkins University in Washington, said on 2 December, satellite images showed construction of a test tunnel at Punggye-ri, on North Koreas east coast where it conducted its three previous nuclear tests.

Im tempted to believe that the fourth tunnel is just a bluff to be able to put pressure in the international community to resume the discussion with them, Lassina Zerbo, head of the Comprehensive Nuclear-Test-Ban Treaty Organisation (CTBTO), said.

North Korea has conducted three underground nuclear tests since 2006. The last, in 2013, drew international condemnation including from China, its main political ally. Isolated North Korea is under UN sanctions that prohibit trade that can fund its arms programme.

Diplomatic talks among six countries including the US and North Korea aimed at ending its nuclear programme produced a deal in 2005 from which the North has since walked away. North Korea has been steadily working on its nuclear programme, but a fourth test is not seen as imminent.

While a new tunnel at the site could well indicate North Korea was preparing a test, the timing would probably depend on political factors more than technical ones, said Jeffrey Lewis, author of the 38 North report. The Norths agreement with South Korea in August to work towards easing tension and improving ties also meant a test was less likely, said Zerbo.

Under those circumstances one would not anticipate that North Korea will go for a new testing or explosive testing at the time when theyre engaged in discussions with their brothers from the South, Zerbo said.

Zerbo added that North Korea is the only country to have conducted a nuclear test explosion in the 21st century and the world is too civilised for anyone to resume testing.

The international community is making all it can to constrain any new comer in the nuclear weapon world. And North Korea receives enough signals from the international community that the intention is not of this 21st century, and that resuming nuclear test explosion will not help them anyhow to put more pressure in the international community, he said.

More than 160 countries have ratified the Comprehensive Nuclear-Test-Ban Treaty since 1996.