While North Korea's latest nuclear test shows it is making steady progress toward a deliverable nuclear weapon, it is not clear whether the international community or China, its greatest trading partner and ally, have enough influence to persuade it to stop, analysts say.
Based on seismic evidence, "we can say with certainty they're getting better at building their nuclear device," said Robert Avagyan, a research analyst at the Institute for Science and International Security, a think tank focused on controlling the spread of nuclear weapons.
But North Korea's economy is so isolated that even China, North Korea's No. 1 trading partner, political ally and patron, has little influence on North Korean decision-making, says James Acton, a proliferation expert at the Carnegie Endowment for International Peace.
"North Korea's economy is extremely isolated and focused on self-reliance," Acton said. Despite growing trade with China, there is still "probably not much leverage there."
North Korea's third nuclear test produced a blast of about 10 kilotons, about twice as powerful as the 2009 test and almost 10 times more powerful than the first test, in 2006, Avagyan said. For comparison, the Hiroshima bomb was a 12- to 20-kiloton blast, he said.
North Korea said the device it exploded was smaller than previous devices, but the question remains whether it would fit on a ballistic missile of the type that launched a satellite into orbit in December. North Korean officials said after that test that the USA is the target their weapons program is aimed to deter.
The United States, its allies, the United Nations, Russia and China urged North Korea not to proceed with the nuclear test and condemned the test after it occurred. North Korea is already subject to severe international sanctions that limit its trade with most of the world.
Professor Yu Chung Sik, a political expert in China's Shanghai International Studies University, says his country's influence on North Korea is waning. "China has less impact on North Korea than before," Yu said.
But Acton said that sentiment is a self-serving one adopted by Chinese officials who would rather not take action. Even if China had leverage, it probably would not use it for fear of bringing down the North Korean regime, Acton said.
China views its North Korean ally as a crucial buffer keeping the U.S. military from its border.
Avagyan said China may respond to North Korea's defiance by signing on to international sanctions that prevent trade of so-called dual use items that North Korea can use for its nuclear program. China could clamp down on some trade with North Korea, he said.
A network of civilian-owned and North Korean front companies funnels supplies for centrifuges, reactors, testing and delivery devices through China, he said.
"The Chinese are not as strict in their export controls of dual use materials that would benefit North Korea's nuclear program," Avagyan said.
Acton, however, said that China has little control over its remote North Korea border.
"At an official level, the Chinese government isn't providing these items," Acton said. "But the borders are very porous and Chinese border controls are very weak. There's a long history of people moving freely across the border."