South Korean president Moon Jae-in will meet Donald Trump in Washington on Tuesday in a bid to salvage a potentially historic summit next month between the US leader and North Korea's Kim Jong Un.
The hastily arranged White House trip is intended to reassure the Trump administration, which has indicated concern that next month's summit could fail, and irritation at Mr. Moon's own performance as a go-between.
"It now seems Mr. Moon is the most anxious that the talks between Mr. Trump and Mr. Kim could fall apart," said Kim Jae-chun, a professor at Sogang University in Seoul.
While South Korea has positioned itself as the intermediary between Washington and Pyongyang for months, tensions have increased in recent days over the issue of the denuclearization of North Korea's weapons arsenal.
US officials — in particular John Bolton, Mr. Trump's hawkish national security adviser — see a firm commitment to "denuclearize" as a key first step by Pyongyang, while North Korea has remained vague about how it might denuclearize, despite earlier pledges to do so.
It said last week it would cancel the proposed summit if Washington continued to pressure it to "unilaterally" abandon its nuclear weapons program.
"Mr. Moon will stress [to Mr. Trump] that the US should not push a one-sided denuclearization of North Korea by demanding it first dismantle nuclear weapons in return for compensation later," said Yang Moo-jin, a professor at the University of North Korean Studies in Seoul.
"Mr. Moon will probably tell Mr. Trump that what Kim Jong Un wants is to be treated as a normal leader of a normal nation. And they will discuss how to guarantee the Kim regime's security and how to help develop North Korea's economy."
Pyongyang has been particularly irritated by the proposal made by Mr. Bolton that North Korea should adopt the " Libya model " for denuclearization — a reference to the late Colonel Muammar Gaddafi's 2003 decision to scrap his country's fledgling nuclear program.
The very idea of the Libya model of abandoning nuclear weapons in exchange for aid is known to infuriate officials in Pyongyang, who believe that the deal paved the way for Gaddafi's overthrow and murder in 2011.
By contrast with his national security adviser, the US president last week dismissed the Libyan experience as a model for any eventual deal with Pyongyang, instead promising Mr Kim "very strong" protections if he agreed to dismantle the country's nuclear program.
Even politicians in Seoul have expressed angst over Mr. Bolton's proposal, which has long been a taboo topic.
"Because of Bolton's unreasonable talk about the Libyan model, there is now a red light in the inter-Korean and US-North Korea talks," said Woo Sang-ho, a lawmaker with the ruling Democratic party.
"Trump's talk of guaranteeing the security of the North Korean regime is the complete opposite of Bolton's Libyan solution . . . I think the momentum for talks will only return after this issue gets cleared."
Bong Young-shik, a North Korea expert at Yonsei University in Seoul, said: "Many officials in the Moon administration hate John Bolton because of [past] bitter experiences . . . He is known as a hardliner who does not work on a case-by-case basis."
Mr. Moon last month met Kim Jong Un in a landmark summit that ended with a declaration to reduce hostilities and denuclearise the Korean peninsula.
However, the exact meaning of denuclearization was never clarified and Mr. Moon now faces skepticism from the US that he over-interpreted North Korea's desire to denuclearize.
"Mr. Trump already seems concerned that Mr. Moon misinterpreted Kim Jong Un's message or intention," said Prof Bong. "Mr. Moon runs the risk of losing his credibility."
Pyongyang has long sought to sow dissension between Washington and Seoul, which have been allies since the Korean war.
Some experts have expressed fear that if the US rushes into the June 12 summit without sufficient preparation, the meeting will inevitably fail and the risk of conflict on the Korean peninsula will once again increase.