Satellite images of North Korea's underground nuclear test site suggest that the regime is ready and able to carry out at least three additional detonations with no advance warning.

The warnings that Pyongyang is able to conduct more tests just days after the September 9 detonation of what experts estimate was a 10-kiloton device - the largest it has ever tested - come from the South Korean military and images from commercial satellites analyzed by experts and posted on the 38 North website, run by the US-Korea Institute at Johns Hopkins University.

Joel Wit, a senior fellow at the institute, wrote in an opinion article for The New York Times that the regime of Kim Jong-un had prepared the Punngye-ri nuclear proving grounds for "at least" three more tests. He added that any such demonstration by the North might be timed to coincide with the 10-year anniversary of the regime's first successful nuclear test on October 9, 2006.

"It is impossible to predict with any certainty a time frame or the type of test they will carry out as it's all very speculative, but all North Korea's behavior and testing to date is consistent with their program to develop their nuclear capabilities," Daniel Pinkston, a professor of international relations at the Seoul campus of Troy University, told DW.

Motivated regime

"And it is clear that the leadership is very motivated to expand its nuclear capabilities and testing is the whole point of that," he said.

"Clearly there are considerable political ramifications to this course of action, both domestic and international," Pinkston pointed out. "But the North Korean leadership is willing to bear those costs and appears to be insensitive to the international costs it is facing over both its nuclear and ballistic missile tests."

Pinkston said it should come as "no surprise" should Kim Jong Un's regime go ahead with more tests, whatever the outcome of discussions within the United Nations Security Council on the application of even more sanctions.

And the fact that Pyongyang appears to be speeding up its nuclear tests "probably indicates they have more fissile material than many people have previously estimated, possibly from another clandestine uranium enrichment facility that they have been running for some time," the analyst said.

'Strong message'

Speaking in New York on September 14, UN Secretary General Ban Ki-moon called on the international community to send a strong message to North Korea that nuclear and missile tests are unacceptable.

"Never in the past that I have seen such kind of heightened tension on the Korean Peninsula," he said at a press conference marking the opening of the UN General Assembly.

"So it is very important that the United Nations Security Council should be united and take urgent actions to prevent, first of all, the provocative actions by DPRK," he noted, using the initials of the North's official name, the Democratic People's Republic of Korea.

Pyongyang has made it clear, however, that it has no intention of backing down in the face of international criticism and an anticipated ratcheting up of the existing sanctions imposed on the regime, even when an ally like China joins those sanctions.

"Neither sanctions nor provocation nor pressure can ever bring down the position of the DPRK as a full-fledged nuclear weapons state, and the high-handed political and military provocations of the enemies will only invite a merciless nuclear strike, which will lead them to final ruin," the state-run Korea Central News Agency said in an article quoting a spokesman for the Korea Asia-Pacific Peace Committee.

But Toshimitsu Shigemura, a professor at Tokyo's Waseda University and an authority on the North Korean leadership, believes there may be an element of bluff in the statements emerging from Pyongyang.

"They are very afraid of China imposing harsh sanctions," he told DW. "They particularly fear China halting supplies of oil, which would bring their industry and military to a complete halt."

There have been hints, however, about Pyongyang's weapons programs. "Some years ago, the North said its strategy was to complete the development of its nuclear arsenal and then declare a halt to the tests, at which point it would propose negotiations with the US," Shigemura said.

Call for talks

"I believe that they are right now pushing ahead to complete their nuclear weapons and the missiles to deliver them and that they will soon call for talks." Kim appears to be walking something of a political tightrope at home, Shigemura believes, after shifting resources and effort away from the military in favor of shoring up the national economy.

It is a policy that could foment dissatisfaction among the military, he added, although Kim's ruthlessness - human rights organizations believe that at least 60 senior officials have been executed over the last year and hundreds sent to labor camps - means that a revolution is "unlikely," he said.

Pinkston concurs that East Asia is "entering an era that is extremely unstable," adding that the two sides appear to be degenerating into a dangerous escalatory cycle, while there is also the possibility of a miscalculation on either side leading to a serious clash.

"My view is that as North Korea acquires greater capabilities and greater confidence in those capabilities, they will seek ways to obtain benefits," he said.

North Korea is a "dissatisfied and revisionist power" that still wants to unify the peninsula under its control and wants to "complete the revolution" in the South, he added.