South Korea should make a strategic decision in the face of intensifying rivalry between the United States and China, an American expert said Friday, warning that Seoul has been increasingly isolated from the region's multilateral diplomacy due to its "ambivalent" stance.

Victor Cha, Korea chair at the Center for Strategic and International Studies, made the point in a presentation for a seminar on the South Korea-US alliance, saying that such isolation will ultimately leave South Korea to deal with China alone.

"Hedging or a 'muddle-through' approach' is not in the interests of Seoul, it will not be good for the alliance and it will invite even more Chinese pressure," Cha said. "And dealing alone with China's challenge to supply chains, 5G networks and the rules-based liberal order is much more difficult than doing so with fellow democracies."

The seminar took place as President Moon Jae-in was in Washington for one-on-one talks with US President Joe Biden, with COVID-19 vaccine cooperation, North Korea and other alliance issues expected to be high on the agenda.

Referring to a flurry of communications between Seoul and Washington that took place from the onset of the Biden administration, Cha said such a volume of exchange is "akin to starting out a marathon at a sprinter's pace," and that it is partly aimed at bringing South Korea "back into the fold of diplomacy with the major democracies in Asia."

New networks are forming in Asia among "like-minded countries" and these networks are becoming "inextricably intertwined over a series of overlapping issues," he said, citing a series of regional initiatives, including the US-led Quad forum which is widely seen as keeping a growing China in check.

"It is time for Korea to have a national discussion about its strategic choices in an era of US-China competition," Cha said. "Opting in or out of the new coalitional diplomacy among the democracies of Asia needs to be a strategic choice by Seoul, not an unintentional outcome."

Amid growing competition between the two superpowers, Foreign Minister Chung Eui-yong has said that the US and China are "by no means a subject of choice," and that Seoul will seek to "harmoniously" develop relations with China based on the robust alliance with the US 

During the forum, Cha claimed that the US "reportedly invited Korea to become a member of the Quad grouping but Seoul declined."

The foreign ministry immediately rejected the claim.

"As our government has repeatedly said, we have not received any invitation from the Quad members to join the forum," a ministry official said.

White House Asia czar Kurt Campbell also said in a recent interview with Yonhap News Agency that the US administration currently has "no plans to expand the Quad." (Yonhap)