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.
"China is developing what could be the world's longest range air-to-air missile," said John Chipman, director-general and chief executive of the IISS.
Chipman made his comments at a press conference last week highlighting IISS's annual Military Balance report, a global assessment of military capabilities and defense economics from IISS.
Overall, IISS believes China is gaining significant ground in the air arena. It pointed out that China's budget on military expenditures in 2016 of $145 billion is about 1.8 times higher than South Korea and Japan combined.
"Western technological superiority, once taken for granted, is increasingly challenged," said Chipman. "We now judge that in some capability areas, particularly in the air domain, China appears to be reaching near-parity with the West."
According to IISS research, at least one of the missile systems China is developing have no Western equivalent.
The Chinese air force's PL-10 "dogfighting" missile is seen as one of the country's most potent guided weapons. There's also China's long-range PL-15 advanced missile, which has been tested on fighters and destroyed drones.
"When it enters service, this new system will hold at risk large, high-value targets like tankers and AWACS aircraft platforms that would traditionally safely loiter outside the range of current air-to-air weapons," Chipman said.
The PL-15 developmental missile is longer than China's current air-to-air radar-guided weapon system known as the PL-12, a missile developed more than a decade ago with help from Russia.
China's domestic military development and advanced research has grown in the past few years to the point where the communist nation is developing and manufacturing its own weapon systems, no longer relying as much on Russia, according to IISS.
The air-to-air PL-15 missile's main rival in the U.S. arsenal is the AIM-120, also known as AMRAAM (or Advanced Medium-Range Air-to-Air Missile) and manufactured by Massachusetts-based defense contractor Raytheon.
Even America's next-generation F-35 stealth fighter — a fifth-generation fighter — could be put to the test by some of the advanced weapons under development by China, according to IISS.
Douglas Barrie, a senior fellow for military aerospace at IISS, said the pace and introduction of China's development of air-to-air missile technology is "almost unheralded." He said China's military has "a very, very capable palate of air-to-air weapons. In terms of what this means for the F-35, well it makes the air environment that much more difficult."
China also has been developing its own fifth-generation fighter, the J-20. The first two J-20 stealth fighters are now in test units, according to IISS.
A second stealth fighter is getting tested in China, the FC-31 Gyrfalcon. The plane is expected to eventually become available for overseas exports.
"Beijing is now beginning to offer for export some of its modern military systems across the globe," said Chipman. "There is a growing proliferation of lethality, and the increasing sophistication of these systems risks complicating Western states' military options."