North Korea is showing no signs of preparing for a new nuclear test, a US think tank said Friday, citing recent satellite imagery.

However one or more tunnels at the Punggye-ri nuclear test site are complete and ready for another test should Pyongyang decide to carry one out, the US-Korea Institute at Johns Hopkins University said.

On its closely-watched 38 North website, the institute said commercial satellite pictures of the Punggye-ri test site revealed no signs of test preparations.

"As a result, a fourth nuclear test seems unlikely in the near-term, for at least the next two to three months," 38 North said.

"However, it is quite possible that one or more tunnels at the facility are sufficiently complete to be readied for another nuclear test should Pyongyang make the political decision to move forward."

The North has so far conducted three nuclear tests at the Punggye-ri site in its northeast, in 2006, 2009 and 2013.

Pyongyang in November threatened to carry out its fourth test in response to a UN resolution condemning its human rights record.

But last week it offered to "temporarily" suspend any future test if the United States cancels its annual joint military drills with South Korea this year.

The United States immediately rejected the offer, calling it an "implicit threat".