SEOUL — As Secretary of State Mike Pompeo arrived at the North Korean capital of Pyongyang on Friday, officials in South Korea were quietly — and probably nervously — watching the first high-level, face-to-face interaction between the United States and North Korea since President Trump met with Kim Jong Un in Singapore on June 12.

For South Korean President Moon Jae-in, there is reason to worry. A prominent advocate for U.S.-North Korea talks, the soft-spoken South Korean leader played a pivotal role in bringing the brash Trump and the once-reclusive Kim together for last month’s historic summit.

If talks between the United States and North Korea were to break down, it could spell doom, too, for Seoul’s own ongoing negotiations with Pyongyang. That would in turn cause major problems for Moon, whose sky-high approval ratings can in part be attributed to his savvy handling of both Trump and Kim.

North Korea’s commitment to denuclearization has come under intense scrutiny in the weeks since the Singapore summit. U.S. intelligence officials told The Washington Post last week that North Korea does not intend to fully surrender its weapons stockpile, while recently released commercial satellite imagery appeared to show North Korea expanding a missile-manufacturing plant.

Reuters reported Thursday that South Korean officials had been offering advice to their U.S. counterparts on how to deal with these issues, with one senior official from Seoul visiting Washington this week and suggesting that the United States move away from its aim of “complete, verifiable and irreversible denuclearization” toward a softer approach, according to the news agency.

Kim Eui-keum, a spokesman for the presidential Blue House, would not respond directly to the report when asked about it Friday. “What I can say is that the South Korea and the United States are constantly communicating on such issues concerning denuclearization of the Korean Peninsula and the settlement of permanent peace,” he told reporters, adding that the two countries were “making efforts to come up with a constructive solution to the issue of denuclearization.”

This cautious approach of the South Korean president’s office reflected growing skepticism about North Korea’s willingness to give up its nuclear weapons, said Kim Sung-han, a former vice foreign minister under conservative president Lee Myung-bak who is now dean of Korea University’s Graduate School of International Studies.

He added that “the mixed signals from Washington” were probably another reason for the stance, pointing to apparently differing time frames for North Korean denuclearization offered by Pompeo and White House national security adviser John Bolton. “The Blue House is not quite sure which side represents President Trump’s mind.”

However, Moon Chung-in, a professor at Yonsei University and an adviser to the South Korean president, said that the Blue House had always been clear that it would leave issues related to denuclearization to the United States and North Korea. “He has been a faithful facilitator,” he said of the South Korean leader, adding that the president had “sometimes mediated between Pyongyang and Washington when there was a stumbling block between the two.”

Instead, South Korea was taking charge of issues related to peace and prosperity on the Korean Peninsula and reunification, Moon Chung-in added. The issues are deeply interlinked. Before his election in May 2017, Moon Jae-in had campaigned on a policy of warmer diplomatic and economic ties with North Korea.

These campaign promises were swiftly tested, as North Korea began conducting regular weapons tests and Trump warned of “fire and fury” in response. Things changed at the start of this year, when Kim Jong Un — in a New Year’s address that highlighted the technological leaps made in his weapons testing — suggested that he might let North Korean athletes attend the 2018 Winter Olympics in PyeongChang, South Korea, in February.

South Korean President Moon Jae-in, right, and North Korean leader Kim Jong Un meet in the truce village of Panmunjom inside the demilitarized zone separating the two Koreas on April 27. (Korea Summit Press Pool/Reuters)

In the flurry of diplomatic activity that followed, South Korean diplomats were the ones conveying Kim Jong Un’s desire to meet Trump. Moon Jae-in himself met with his North Korean counterpart on April 27 in the demilitarized zone that divides the peninsula.

The two leaders agreed to a work toward a variety of aims — including, notably, “a nuclear-free Korean Peninsula,” as well as economic cooperation and efforts to reunite families that were split by the 1950-1953 Korean War.

The South Korean government’s efforts with North Korea have proved remarkably popular with its public. One poll conducted in early May found that 9 out of 10 South Koreans approved of the inter-Korean summit, while the president had an approval rating of 86 percent. It has dipped, however, in recent weeks, hitting 69 percent, as doubt about North Korea’s intentions appeared to spread.

Though it has slipped only slightly at the moment, polling experts suggest that things could get far worse. “Moon’s popularity is a result of the rapprochement of the United States and North Korea,” said Kang Won-taek, a professor at Seoul National University. “If that relationship collapses, it will probably precipitously go down.”

And ultimately, that relationship doesn’t lie in the hands of South Koreans, but with the U.S. and North Korean interlocutors. Moon Chung-in noted that while the current relationship between South Korea, North Korea and the United States was conducive to finding peace for all parties, that could well change.

“Land mines are everywhere on the way to peace on the Korean Peninsula,” he said.