North Korea's allies, China and Russia, have expressed worries that the anti-missile system's radar will be able to track their own military capabilities, and that the deployment will do nothing to lower temperatures on the Korean peninsula.
China "means what it says" when it says it will consider countermeasures against the planned US deployment of an advanced anti-missile system in South Korea, the defense ministry said on Thursday.
China, North Korea's neighbor and lone major ally, has repeatedly expressed anger at the United States and South Korea for their decision to deploy the US Terminal High Altitude Area Defence (THAAD) system in the South to counter missile and nuclear threats from North Korea.
The South Korean defense ministry said it would announce a new location for the system on Friday, after opposition from residents for the initial site choice.
Around 900 South Koreans shaved their heads in August to protest against their government's decision to place the missile defense system in the southeastern county of Seongju.
Chinese Defence Ministry spokesman Yang Yujun said China's opposition to THAAD was clear.
"We will pay close attention to relevant developments, and consider taking necessary actions to protect national strategic security and the regional strategic balance," Yang told a monthly news briefing.
"What needs to be stressed is that Chinese people mean what they say," he added, without elaborating.
Beijing worries the system's radar will be able to track its own military capabilities, and that the deployment will do nothing to lower temperatures on the Korean peninsula.
Russian has expressed similar opposition.
North Korea, which has threatened a "physical response" against the THAAD decision, has conducted a series of military technology tests this year, including a fifth nuclear test this month, in defiance of UN Security Council sanctions that were tightened in March.
US to deploy anti-missile system in South Korea 'as soon as possible'
Beijing's latest warning comes two days after the United States announced it will speed up deployment of the THAAD anti-missile system to South Korea, adding that it will be stationed there "as soon as possible."
A Pentagon spokesman, Commander Gary Ross, had said THAAD would be deployed "as soon as feasible," but declined to give a specific timeline.
Daniel Russel, assistant secretary of state for East Asia, told a congressional hearing the United States was in discussions with international partners, including the European Union, to deny North Korea access to international banking infrastructure after its recent nuclear and missile tests.
He also said the United States and its allies Japan and South Korea had been working to cut off North Korean revenue streams from coal and overseas workers and were considering further joint action.
Russel told the House subcommittee for Asia the timing of the deployment of the Terminal High Altitude Area Defense system was a Pentagon matter.
But he added: "Given the accelerating pace of North Korea's missile tests, we intend to deploy on an accelerated basis. I would say as soon as possible."
Asked if the deployment was a "done deal," Russel replied: "Yes."