A Terminal High Altitude Area Defense (THAAD)

South Korea and the United States said on Friday that they will deploy an advanced missile defence system in South Korea to counter a threat from North Korea, drawing sharp and swift protest from neighbouring China.

“The Terminal High Altitude Area Defence (THAAD) anti-missile system will be used only as protection against North Korea’s growing nuclear and ballistic missile capabilities”, the South’s Defence Ministry and the U.S. Defence Department said in a joint statement.

Beijing said on Friday it lodged complaints with the U.S. and South Korean ambassadors over the THAAD decision.

China said the system would destabilize the security balance in the region without achieving anything to end the North’s nuclear program. China is North Korea’s main ally but opposes its pursuit of nuclear weapons and backed the latest U.N. sanctions against Pyongyang in March.

China strongly urges the United States and South Korea to stop the deployment process of the THAAD anti-missile system, not take any steps to complicate the regional situation and do nothing to harm China’s strategic security interests,” the foreign ministry said in a statement.

Selection of a site for the system could come in weeks and the allies were working to have it operational by the end of 2017, a South Korean defence ministry official said.

The THAAD will be deployed to U.S. Forces Korea, to protect the alliance military forces from North Korea’s weapons of mass destruction and ballistic missile threats,” the joint statement said.

The United States maintains 28,500 troops in South Korea, a legacy of the 1950-53 Korean war.

When the THAAD system is deployed to the Korean Peninsula, it will focus solely on North Korean nuclear and missile threats and would not be directed towards any third party nations,” the statement also said.