For days, the official Chinese news media has warned that deployment of Thaad could lead to a “de facto” break in relations with South Korea and urged consumers to boycott South Korean products. The Chinese authorities recently forced the closing of 23 stores owned by Lotte, a South Korean conglomerate that agreed to turn over land that it owned for use in the Thaad deployment, and hundreds of Chinese protested at Lotte stores over the weekend, some holding banners that read, “Get out of China.”

Xinhua, the official Chinese news agency, warned that Thaad “will bring an arms race in the region,” likening the defensive system to a shield that would prompt the development of new spears. “More missile shields of one side inevitably bring more nuclear missiles of the opposing side that can break through the missile shield,” it said.

But in another article, the news agency rebuked North Korea, saying it must “face the reality that it can neither thwart Washington and Seoul nor consolidate its security in a breeze with its immature nuclear technology.”

The United States’ decision to deploy the missile technology brought new scrutiny to China’s policies toward North and South Korea and suggested that its attempts to please both countries in hopes of averting a crisis had fallen short.

“To put it bluntly using a common Chinese expression, it has wanted to have a foot in two boats,” said Deng Yuwen, a current affairs commentator in Beijing who has sharply criticized North Korea.

Yang Xiyu, a former senior Chinese official who once oversaw talks with North Korea, said China was worried that the deployment of the system would open the door to a broader American network of antimissile systems in the region, possibly in places like Japan and the Philippines, to counter China’s growing military as much as North Korea.

“China can see benefits only for a U.S. regional plan, not for South Korea’s national security interest,” he said.