North Korea conducted its third underground nuclear test Feb. 12. A December rocket launch to orbit a satellite raised concerns about the test as similar launch efforts in 2006 and 2009 coincided with underground detonations.
Blog 38 North from Johns Hopkins notes that satellite imagery of the nuclear test facility show possible signs of human activity three days after the test.
"It remains unclear whether renewed activity at the site is normal for the days after a nuclear detonation or if it is an indication of Pyongyang's intention to conduct another test in the near future," the report states.
The recent detonation was said to be of a smaller but more powerful device than those tested in 2006 and 2009. Johns Hopkins researchers say North Korea doesn't have the ability to equip an intercontinental ballistic missile with a nuclear warhead, however.
A source in the Chinese government told South Korea's Yonhap news agency on condition of anonymity that Pyongyang is waiting for action from the U.N. Security Council before it decides to conduct a fourth nuclear test.
"Whether the North conducts more tests is a matter of political deliberation," the source said.