North Korea is notorious for its outlandish and apocalyptic threats against the U.S., but it has now delivered a rare verbal salvo against China, a country seen as one of its only allies on the planet.
Kim Jong Un's regime scolded Beijing, alleging it acted with "insincerity and betrayal" in comments about Pyongyang's burgeoning nuclear and ballistic-missile program.
The neighbors — one a vast, economic juggernaut, the other an impoverished, isolated pariah — have long been locked in an uneasy balancing act.
But last week's comments may be an indication that this six-decade symbiosis is in danger of falling apart.
As Jia Qingguo, dean of the Department of Diplomacy at China's Peking University, put it: "China and North Korea's relationship is at a crossroads."

What happened?

North Korea's rare outburst came in a May 3 comment piece carried by the state-run Korean Central News Agency, or KCNA.
The agency, which is tightly controlled by the Kim's government, accused China of committing "a wanton violation of the independent and legitimate rights, dignity and supreme interests" of North Korea.
It said its "strategic interests have been repeatedly violated due to insincerity and betrayal on the part of its partner" and warned of "grave consequences."
This was in response to China's state-media floating the idea of further sanctions against North Korea in response to its nuclear ambitions.