North Korea's main ally says it "firmly opposes" Pyongyang's purported hydrogen bomb test and is monitoring the environment along its border with the North near the test site. China plans to summon North Korea's ambassador in Beijing to the Foreign Ministry to lodge a strong protest, spokeswoman Hua Chunying told reporters at a daily briefing Wednesday. China made a similar protest after the North's last nuclear test in 2013. Wednesday's reported test was performed in defiance of the international community and in contravention of its earlier denuclearization promises, Hua said. "North Korea should stop taking any actions [that] would worsen the situation on the Korean peninsula," she told reporters.
Environment bureau technicians were monitoring conditions near the border, but air quality near the bomb site was within the normal range, Hua said, adding that in the longer term, North Korea should return to long-stalled six-nation denuclearization talks hosted by China. The test was also denounced by the European Union and South Korea, which called it a "grave provocation," the BBC reports. Pyongyang, meanwhile, said the test was a complete success that has made the country an advanced nuclear nation. "It is just to have H-bomb as self-defense against the US having numerous and humongous nuclear weapons," a North Korean state broadcast said, per the Guardian. (Here's more on the science of Pyongyang's H-bomb claim.)