The mysterious death of Kim Jong Un's half brother removed a potential avenue for China to press the North Korean leader to rein in his nuclear ambitions.

Kim Jong Nam, 45, lived out of North Korea for many years and had close links to China. He started families in both Beijing and Macau, and had the protection of Chinese authorities, according to a South Korean lawmaker who was briefed on intelligence reports.

His murder at a Malaysian airport on Monday in circumstances akin to a spy novel adds to concern that Pyongyang's actions risk a major geopolitical miscalculation. Jong Un's repeated nuclear and missile tests — most recently on Sunday — have caused unease both in the U.S. and China, and put Beijing in a difficult spot as North Korea's prime benefactor and ally.