South Korea should be careful not to be overly dependent on China, a key sourcing destination for Seoul, as Beijing could leverage that to get what it wants in a world split between free democracies and authoritarian regimes, NATO Secretary-General Jens Stoltenberg said in Seoul on Monday.

The visit by the chief of the 30-member military alliance based in Brussels, Belgium -- the second time since 2017 -- is the latest move by the Western coalition trying to push back against longtime adversaries like Russia by rallying major Asian democracies. Japan is Stoltenberg’s next stop.

Speaking at the Chey Institute for Advanced Studies in Seoul, the first stop of his two-day trip that started Sunday, the NATO chief drew on a German example of how Russia had weaponized gas supplies, warning of security implications from “commercial decisions.”

“To be too dependent on specific commodities -- specific raw materials, rare earth minerals for instance -- makes us vulnerable. If we start exporting advanced technologies, China and Russia can later on use them to threaten us. Then we make ourselves vulnerable,” Stoltenberg said.

“If we allow China to control critical infrastructure, we become vulnerable,” he said in response to questions over China’s retaliation against Korea if it expands ties with NATO. Though not an adversary, China is still a “challenge” that NATO has recently given higher priority to, according to the alliance chief, who labeled the county everything against free democracies stand for.

Taking into account how business decisions carry security consequences is crucial, Stoltenberg noted, but that does not mean abandoning free trade. He did not elaborate on ways for Seoul to manage trade ties with Beijing -- Korea’s biggest trading partner.

As long as authoritarian powers do not relinquish their control over nuclear weapons, nuclear deterrence cannot be ruled out, the NATO chief added in support of the “extended deterrence” Korea and the US maintain. The term refers to US support involving its nuclear umbrella and strategic assets like bombers and fighters, all meant to prevent outside aggression.

Korea, Stoltenberg said, should do more to step up its military support for Ukraine as other countries have already gone as far as reversing their previous policy of not providing weapons to countries in conflicts. Germany said last week it would send Leopard 2 tanks.

Stoltenberg described arms support as crucial in bringing closure to the Russian invasion of Ukraine, a mission he said all countries embracing democracies should help achieve. Later in the day, the NATO chief met with Defense Minister Lee Jong-sup and President Yoon Suk Yeol. Yoon attended a NATO summit in June last year, as the first South Korea leader to do so.