Story highlights "You gotta work on North Korea," Trump told a Chinese official

North Korea has successfully developed nuclear weapons

Washington (CNN) President Donald Trump believes the "greatest immediate threat" to the US is North Korea and its nuclear program, a senior administration official told reporters.

Trump has already called on China to take action to rein in North Korea, over which China has considerable influence and leverage, the official said.

"You gotta work on North Korea," Trump told a Chinese official on February 27, the senior administration official said, apparently pointing to a brief meeting at the White House between Trump and Chinese State Councilor Yang Jiechi, the highest-ranking Chinese official Trump has met with since taking office.

North Korea has successfully developed nuclear weapons, but still lacks a delivery method, the official said. Still, the US administration is concerned that North Korea could purchase a delivery method.

Trump is not the first US president to be alarmed over North Korea's nuclear program.

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