North Korea is not showing any signs of preparations for a nuclear test despite its apparent threat to do so, a U.S. research institute said.
  

The North said last week that its bomb-making nuclear facilities at the Yongbyon complex have returned to normal operation and are ready to respond to U.S. "hostile policy" toward it with "nuclear thunder," a term apparently referring to a nuclear test.
  

"Despite renewed speculation of a possible North Korean nuclear test, recent commercial satellite imagery from September 7, 2015, shows no sign of nuclear test preparations at the North's Punggye-ri nuclear test site and little or no change at the facility since August," 38 North said in a report dated Friday.
  

The North conducted its three nuclear tests in 2006, 2009 and 2013, all at the Punggye-ri site in the country's northeast.
  

The site's west portal, the site of the 2009 and 2013 tests, has shown little activity since the beginning of this year, particularly in the spoil pile created by what appears to have been the digging of another tunnel, 38 North said.
  

That may mean excavation has been completed or interrupted, it said.
  

Satellite imagery shows there are two new buildings erected at the entrance to the west portal that are likely used to support the guards controlling access to the area, the institute said.
  

In addition to the nuclear test threat, the North also threatened to conduct a long-range rocket launch, possibly around next month's ruling party anniversary, in violation of U.N. Security Council resolutions banning the North from any ballistic activity.
  

Pyongyang has long been accused of using long-range rocket launches as a pretext for test-firing intercontinental ballistic missiles. Experts say long-range rockets and ICBMs are basically the same with differences only in payloads.
  

South Korea and the U.S. suspect that for now, the North is more likely to conduct a long-range rocket launch than a nuclear test, and has urged Pyongyang not to go ahead with a launch or face stronger U.N. sanctions.
  

In the past, the North conducted a rocket test first before using international sanctions and condemnations for the launch as a pretext for going ahead with a nuclear test. (Yonhap)

(责任编辑：新闻中心)