Visiting U.S. Defense Secretary James Mattis and Republic of Korea National Security Office chief Kim Kwan-jin met in Seoul on Thursday and agreed to press forward with deployment of the Terminal High Altitude Area Defense system in the ROK, a move that observers have said may destabilize Northeast Asia.
The Pentagon chief, who arrived in the ROK on Thursday, said the Trump administration will make a top security priority of nuclear threats from the Democratic People's Republic of Korea.
Mattis said before the visit that "no other nation" needs to be concerned about the THAAD system, Reuters reported.
Beijing has firmly opposed THAAD deployment on the peninsula, saying that it will damage China's security interests as well as the regional strategic balance.
Teng Jianqun, a senior U.S. studies researcher at the China Institute of International Studies, said the deployment will compromise the stability of the Korean Peninsula and Northeast Asia.
The ROK is Mattis' first stop on the first overseas trip by a top official in the Trump administration. He plans to leave for Japan after attending more meetings in Seoul on Friday.
Analysts said Mattis' visits to the ROK and Japan show Washington's intention to contain China through bolstering its relationship with Seoul and Tokyo.
Zuo Xiying, a researcher at the National Academy of Development and Strategy at Renmin University of China, said the Diaoyu Islands also are likely to be discussed during Mattis' trip.
The Japanese government illegally purchased the islands located in the East China Sea in 2012, causing China-Japan ties to plummet.
Washington is likely to ask for Tokyo's help in containing China in the East China Sea and South China Sea, he predicted, adding that the U.S. "will make use of all the powers it can" to achieve that goal.
Chu Shulong, an expert on China-U.S. relations at Tsinghua University, said Japan and the ROK remain the two most important countries for U.S. security strategy in East Asia, which is targeted at China, given that Washington "views China as the top country it needs deal with".
However, he pointed out that China and the U.S. don't have to be antagonists, and suggested China work to develop a dialogue and cooperation with the new U.S. administration.
Xinhua contributed to this story.