President Donald Trump took to Twitter on Friday morning to criticize North Korea during a moment of heightened tensions between the two countries, accusing the hermit kingdom and nuclear power of “playing” the United States.

“North Korea is behaving very badly,” he said. “They have been ‘playing’ the United States for years. China has done little to help!

The tweet comes just after Secretary of State Rex Tillerson said in Seoul that the U.S. would not return to the bargaining table to dissuade North Korea’s nuclear buildup, but would consider pre-emptive military intervention as an option. When asked if the U.S. would consider military action to stop North Korea’s nuclear development, Tillerson said “we do not want to, for things to get to military conflict,” but added that “if they elevate the threat of their weapons program to a level that we believe requires action, then that option’s on the table.”

“The policy of strategic patience has ended,” Tillerson said, signaling an end to the Obama Aministration’s strategy of increasing sanctions and covert action in the hopes of dissuading North Korea from further nuclear development. North Korea has conducted nuclear and missile tests, and has publicly boasted that it intends to develop a nuclear-armed ballistic missile that can reach the continental U.S. North Korean leader Kim Jong Un announced on New Year’s Day that the country was preparing to test an intercontinental ballistic missile, and experts say the country’s nuclear program is four to five years away from fully achieving that goal.

Tillerson is expected to travel to China on Saturday.

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Write to Charlotte Alter at charlotte.alter@time.com.