US Secretary of State Rex Tillerson warned of possible military options against the DPRK after ending his trip to Seoul, with Beijing as the next stop of his diplomatic tour.

And Tillerson’s boss in Washington has already been tweeting about China.

China has made no secret of its disdain for the THAAD system. It has long suspected the US will use the anti-missile defense to spy on China, and to assert military dominance in the Asia Pacific region.

On Friday, in response to comments made by Tillerson in South Korea, the Chinese Foreign Ministry reiterated its position that THAAD was not conducive to safeguarding peace and stability.

“The monitoring and early warning radius of THAAD reaches far beyond the Korean Peninsula, deep into the Asian hinterland, and covers a vast territorial area of China, which reaches far beyond the range in coping with the nuclear missile threat,” Hua Chunying, Chinese Foreign Ministry spokeswoman said.

China is urging an immediate stop to THAAD’s deployment, though construction of the system has already begun. The Foreign Ministry also criticized Tillerson for rejecting talks with the Democratic People’s Republic of Korea, and for suggesting that the US might be forced to take preemptive actions against the DPRK over its nuclear program.

China insists diplomacy through the now-suspended Six-Party talks continues to be the best course for resolving tensions on the Korean Peninsula. And when Tillerson meets with Chinese officials over the weekend, he will have to explain what is now the clearest indication of the Trump administration’s policy; what Tillerson called an end to US “strategic patience;” a position that marks a significant departure from the one held by the Obama White House.

Ahead of Tillerson’s arrival in China, his boss, Donald Trump, tweeted: “North Korea is behaving very badly. They have been “playing” the United States for years. China has done little to help!” No doubt that blaming China is not going to go over well in Beijing.

China, which shares a land border with the DPRK and is the largest recipient of the Pyongyang’s exports, maintains various degrees of leverage over the country but has long maintained that Washington doesn’t appreciate its position.

President Trump’s tweet from Washington may ultimately undermine what Tillerson was hoping to achieve in China, or at least throw off what would normally be a carefully choreographed diplomatic dance. This may affect, or even define, an all-important future meeting between Trump and his Chinese counterpart Xi Jinping.