The South Korean flag was raised for the first time at a Nato cyber defence centre in Tallinn, the Estonian capital, on Thursday, when Seoul became the first in Asia to join the group.

Nato's Cooperative Cyber Defence Centre of Excellence trains specialists from member states to work together to fend off cyberattacks and South Korea is the fifth non-Nato member to sign up for it.

South Korea's National Intelligence Service said it had been trying to join the cyber defence centre since 2019 to learn more about threat response strategies and ways to protect key infrastructure, with the broad aim of having world-class abilities to respond to those dangers.

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Although the centre is separate from the Nato command structure, Chinese military analysts said that the addition of its close neighbour and American ally to the group had Beijing worried, seeing it as expansion of the US-led defence alliance in northeast Asia that could threaten Chinese security interests in the region.

China has repeatedly said it is opposed to the enlargement of Nato.

Russia has used the military alliance's eastward expansion to justify its invasion of Ukraine, and Beijing has called for Western countries to consider what it says are Moscow's legitimate security concerns.

Shanghai-based military analyst Ni Lexiong said China saw Nato as being overbearing and expanding, and South Korea's decision to join the centre "definitely does not benefit China".

But Seoul would have considered Beijing's interests and its friendship with China, he said.

Ni said South Korea was a small country surrounded by military giants with conflicting interests and would not actively damage those ties and put its security position in peril.

However, it also faced threats from North Korea that required it to strengthen its defensive capabilities.

"It also needs China to influence and exert pressure on North Korea to restrain the latter's actions," he said.

Ni said China could also be worried about Nato training for South Korea because China would have to show support to North Korea if a conflict erupted on the Korean peninsula.

South Korean president-elect Yoon Suk-yeol, who will take office on Tuesday, has said he will take a harder line on Pyongyang. He is expected to abandon his predecessor's Sunshine Policy of seeking more amicable ties with North Korea.

Yue Gang, a retired People's Liberation Army colonel and military commentator, said China understood that South Korea's entry to the Nato centre did not equate to joining the bloc, but "China is certainly not happy".

"South Korea has not formally joined Nato. It has only entered into a partnership in the area of cyber warfare," Yue said.

"There's nothing much to be said, but China is definitely dissatisfied because cyber warfare is becoming a new battlefield."

Lee Young-hak, a research fellow at the Korea Institute for Defence Analyses in Seoul, said while South Korea would do anything conducive to its security and national defence, it trod carefully when military cooperation concerned what China saw as its "core interests".

These interests include full sovereignty over territories claimed by Beijing, including self-ruled Taiwan, the security of the political system established under the Communist Party and stability in neighbouring regions such as the Korean peninsula.

"The main objective of South Korea in security and national defence is to undermine threats from North Korea's nuclear missiles," Lee said. "To do that, South Korea not only needs to ally with the US but also needs to work with China.

"Therefore, on the basis of the South Korea-US alliance, South Korea is striving for a South Korea-China relationship that can develop harmoniously."

Shanghai-based military analyst Ni agreed, saying that South Korea had to strike a fine balance between its ties with the US and China.

"Whether being friendly or adversarial towards China, there is not much flexibility," he said.

"It's a narrow space for South Korea to manoeuvre, and it cannot jump from one extreme to another. It must rely on the US but also be aware that it cannot get too close because China, a giant country, is its neighbour."

This article originally appeared in the South China Morning Post (SCMP), the most authoritative voice reporting on China and Asia for more than a century. For more SCMP stories, please explore the SCMP app or visit the SCMP's Facebook and Twitter pages. Copyright © 2022 South China Morning Post Publishers Ltd. All rights reserved.

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