President Trump acknowledged the complexity and political sensitivity of the relationship between China and North Korea this week after Chinese President Xi Jinping explained the countries' relationship to him.

Trump told The Wall Street Journal on Wednesday that he was previously convinced China had "tremendous power" over North Korea. But after meeting with Xi last week, Trump said he "realized it's not so easy."

"After listening for 10 minutes, I realized it’s not so easy,” Trump said. “I felt pretty strongly that [China] had a tremendous power over North Korea. But it’s not what you would think.”

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Ahead of his meeting with Xi last week, Trump vowed to pressure the Chinese leader to take a tougher approach to North Korea.

The president's acknowledgement of the situation's complexity comes amid increased tension between the U.S. and North Korea. A U.S. Navy strike group was ordered into the west Pacific near the Korean Peninsula last weekend amid concerns about North Korea's advancing weapons program.

North Korea denounced the strike group's movement as an aggression and threatened a nuclear strike if provoked by the U.S.

"Our revolutionary strong army is keenly watching every move by enemy elements with our nuclear sight focused on the U.S. invasionary bases not only in South Korea and the Pacific operation theater but also in the U.S. mainland," the North Korea's state-run Rodong Sinmun newspaper said.

Foreign journalists in North Korea have reportedly been told to prepare for a "big and important event" on Thursday. North Korean officials have provided no details about the nature of the event or its location, according to Reuters.

Before he left office in January, President Obama warned Trump that North Korea was "the most urgent problem" he was likely to face in his presidency. Along with that warning, Trump has inherited from his predecessor a covert cyberwar against the country's missile program.