Nothing happens in NK without the PRC's tacit approval.
Four North Korean MiG fighters intercepted and threatened to shoot down a U.S. Air Force RC-135 reconnaissance plane in international airspace between the Korean peninsula and Japan on Sunday. The interception came after North Korea accused the United States of conducting spy plane flights infringing on North Korean airspace almost daily since Feb. 21, saying they showed the United States was preparing for war on the communist state.They picked a bad moment to confront the US, since our RC-135 flew in international airspace then.
I haven't heard that the US admits to violatiing North Korean airspace.