The U.S. has expressed pessimism toward North Korean leader Kim Jong-un's proposal of taking a gradual approach to the regime's denuclearization. 

Voice of America(VOA) on Tuesday quoted an unidentified White House official as saying that gradual and step-by-step approaches taken by past U.S. administrations had all failed.

The official told the U.S. international broadcaster that the Trump administration is not interested in allowing the North to buy time. 

The official added the U.S. will act differently this time, stressing that there have to be bold moves and concrete steps toward the North's denuclearization. 

Kim Jong-un emphasized a “phased and synchronized” denuclearization during his summit with Chinese President Xi Jinping in Beijing last month, calling on South Korea and the U.S. to create an atmosphere of peace and stability in tandem with Pyongyang’s own efforts to denuclearize. 

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