China appears "frustrated" with volatile rhetoric from its North Korean allies but is eager to see the regime stay in power as a "buffer state" on its border, US spy chief James Clapper said Thursday. The national intelligence director told lawmakers North Korea's young leader Kim Jong-Un, who has threatened nuclear war with the United States, was testing China's patience. "China is under new leadership and the indication we have is that China is rather frustrated with the behavior and belligerent rhetoric of Kim Jong-Un," Clapper told the House Intelligence Committee.