U.S. President Donald Trump's pitch for a "Indo-Pacific" cooperation system has South Korea walking a tightrope as Seoul strives for a bigger say in America-led regional diplomacy while not risking alienating emerging superpower China.

Trump administration officials have increasingly used the term "Indo-Pacific" as a substitute for "Asia-Pacific," widely seen as a move to counter the growing influence of China by encircling it with a multiple alliance with Japan, Australia and India.

Trump's Asia tour this week heightened the geopolitical prominence of its switch in terminology.

In Japan, Trump and Prime Minister Shinzo Abe declared a "shared vision of a free and open Indo-Pacific" on Monday.

During a summit with President Moon Jae-in Tuesday, he billed the Korea-U.S. alliance a "linchpin for security, stability and prosperity in the Indo-Pacific." Trump is expected to flesh out his new regional vision during his speech at the Asia Pacific Economic Cooperation summit in Danang, Vietnam this week.

The new initiative appears to pose a tough choice for South Korea which is squeezed in between the rivalry involving its traditional ally and biggest trade partner.

Seoul's dilemma was conspicuous on Thursday when President Moon Jae-in's aides made confused remarks about whether it accepts Trump's new approach, from a flagrant rejection to delicate reservation and then active consideration.

"As you can see in the statement... that part was not jointly mentioned by President Moon and President Trump," a Cheong Wa Dae official told reporters in Indonesia.

He was referring to the summit statement released Wednesday, which read, "President Trump highlighted that the United States-Republic of Korea Alliance, built upon mutual trust and shared values of freedom, democracy, human rights and the rule of law, remains a linchpin for security, stability and prosperity in the Indo-Pacific."

The official went on to say, "It was said by President Trump, and President Moon decided not to put his name down for that part."

"We listened to what President Trump had to say, and that was simply because we believe it would not be desirable for us to take part in such a regime for now, considering current global conditions and issues," the official said.

But later in day, Cheong Wa Dae changed its position, saying Seoul and Washington have agreed to "explore areas of possible cooperation" in the Indo-Pacific context.

"Though the concept of the Indo-Pacific region recently proposed by the U.S. does have some similarities with our policy of diversifying our foreign relations, we believed it required additional consultations to see if it was an appropriate concept while pursuing our mutual strategic goals," the presidential office said its official release.

The term "Indo-Pacific" has been used in academic and diplomatic circles since the early 2010s.

In 2010, then U.S. Secretary of State Hillary Clinton used it almost for the first time as a major U.S. policymaker, referring to the larger area and possibly replacing the Asia-Pacific region by including countries with coasts on the Indian and Pacific oceans.

The term is being accepted as a new strategic concept as top Trump aides, including National Security Adviser H.R. McMaster and Secretary of State Rex Tillerson, have repeatedly used it far more conspicuously as they prepared for the president's four-nation Asia sweep.

Japanese leader Abe has been a firm advocate of the broader Asia vision. In August last year he announced his Indo-Pacific initiative, designed to support freedom of navigation, rule of law and fair and mutually beneficial trade mostly among the U.S., Japan, Australia and India.

While the U.S. and Japan seem to be forming a united front in their push for the Indo-Pacific initiative, experts cautioned South Korea against hastily making decisions, calling for more study of the geopolitical impact and diplomatic ramifications.

Some say that joining the initiative might be a good chance for the nation to expand its "space concept" long confined to just Northeast Asia.

"It seems that the Indo-Pacific concept is a joint strategy by the U.S. and Japan to keep China in check and put pressure on it," said Park Jeong-jin, vice director of the Institute for Far Eastern Studies.

"After all those efforts to bring the ties with China back on track, we cannot risk hurting the relations with the big neighbor again."

He referred to the Oct. 31 deal between South Korea and China to mend bilateral ties strained by a prolonged feud over the deployment of a U.S. anti-missile system called THAAD in South Korea. China has opposed the installation, saying that it is part of the U.S.-led global missile defense network and will hurt its strategic security interest.

"We cannot say anything without China in Northeast Asia. Given that it is the largest country that has the biggest influence on us except for Japan in this region, we should think twice before joining such a move that could put pressure on it," he said.

Woo Jung-yeop, a researcher at the Sejong Institute, cautioned against any hasty decisions.

"It is not something that we have to decide right away," he said. "It seems undesirable to talk about joining an initiative like that at a time when we are seeking to mend ties with China and hold a summit with its leader."

Some experts countered that it could be a "good chance" to break South Korea's "confinement" to a relatively small space of Northeast Asia and go into a larger region where it can have closer ties with more countries in various areas.

They still emphasized that the Seoul government should "do its homework" in defining its own Indo-Pacific concept in a way that it will be focused on expanding exchanges in trade, economy and other areas unrelated to security issues.

"Our country has been confined to the Northeast Asia region for a long time, which has restricted our concept of space just to and around the Korean Peninsula," said Son Yul, a professor at Yonsei University.

"We don't have any reason to reject the Indo-Pacific concept. If it is not aimed against China and it is focused on diverse maritime cooperation without security or military aspects, we have no reason not to join it," he added.

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