Terminal High-Altitude Area Defense (THAAD), an advanced missile system, is launched during a successful intercept test in the U.S. Pacific in 2013.

China's military stepped up its criticism this week of South Korea's plans to deploy an advanced anti-missile radar system.

Xinhua, the official press agency for China, also vowed that its "armed forces will make the necessary preparations and resolutely safeguard the nation's security."

The THAAD missile defense system, manufactured by U.S. defense giant Lockheed Martin, is expected to be deployed on the Korean Peninsula to defend against the threat of a North Korean missile attack. Earlier this month, North Korea test fired a ballistic missile as President Donald Trump was meeting with Japan's Prime Minister Shinzo Abe.

U.S. Navy Commander Gary Ross, a Pentagon spokesman, told CNBC on Friday: "The bottom line is we're not going to get into a debate in the public sphere. However, we have reiterated through direct meetings that THAAD is purely a defensive weapon. There's really nothing for China to be concerned with regards to its deployment."

THAAD, which stands for Terminal High-Altitude Area Defense, is designed to protect against both short and medium-range ballistic missile attacks. The Pentagon official said that THAAD interceptor technology is "highly accurate."

Earlier this month, U.S. Defense Secretary James Mattis visited Seoul where he restated American support for South Korea and defensive measures such as deploying THAAD to protect against the growing nuclear and ballistic missile threat from North Korea.

No firm date has been provided when the U.S. will deploy the THAAD system. The Pentagon spokesman said Friday the "deployment will happen as soon as feasible."

The Seoul government gave the green light to deploy the system last summer but that was before the impeachment of Park Geun-hye, South Korea's suspended president. The political crisis and change in leadership could ultimately result in a change in policy.

China's press agency on Thursday quoted a spokesperson for the Ministry of National Defense as saying the THAAD system "will gravely undermine the regional strategic balance and the strategic security interests of countries in the region, including China and Russia."

The comments come as a U.S. aircraft carrier strike group patrols the South China Sea to improve "readiness," according to the U.S. Navy.

The Chinese navy also is in the region to carry out a "counter-attack drill," according to the newspaper run by China's People's Liberation Army. The same paper reported that China is close to completing its second aircraft carrier.

Meantime, China is rapidly developing missile technology of its own that some see as a potential threat to the West, according to the International Institute for Strategic Studies, a global defense think tank.