U.S. President Donald Trump is keeping the pressure on China to take the lead in resolving concerns over North Korea's expanding nuclear weapons program.

In a Twitter message on Friday, Trump said "nothing is easy," but China is North Korea's economic lifeline and if it wants to "solve the North Korean problem" it will.

Trump has emphasized China's role in dealing with the North since last year and has warned Beijing that the U.S. will act alone if China doesn't help.

Lately, however, Trump has been sending encouraging and prodding messages toward China saying it's making an effort.

During a joint news conference with Italian Prime Minister Paolo Gentiloni at the White House on Thursday, Trump praised Chinese President Xi Jinping for working hard to increase pressure on Pyongyang, adding he has great respect for Xi.

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