SEOUL (Reuters) - South Korean President Moon Jae-in has been riding high after a string of successes with North Korea, seeing his popularity surge after his historic meeting with Kim Jong Un as he looks ahead to the U.S.-North Korea summit he helped engineer next month.

FILE PHOTO: North Korean leader Kim Jong Un and South Korean President Moon Jae-in deliver a statement at the truce village of Panmunjom inside the demilitarized zone separating the two Koreas, South Korea, April 27, 2018. Korea Summit Press Pool/Pool via Reuters

But just days before a key meeting with U.S. President Donald Trump, Pyongyang has made Moon’s role as a diplomatic go-between much harder, calling his government “ignorant and incompetent” and pulling out of inter-Korean talks.

Moon heads to Washington next week with the daunting task of crafting a unified approach between the two allies ahead of the June 12 meeting between Trump and Kim in Singapore.

While publicly supporting Trump’s campaign of sanctions and military threats, Moon has long called for reconciliation with the North and has pushed Washington to engage with Pyongyang’s overtures.

North Korea’s threat this week to scrap the Trump summit if Washington continues to press for unilateral denuclearization and complaints about U.S.-South Korea military drills has done little to advance Moon’s hope for a peace deal.

“Moon did an impressive job building up political capital with both leaders - with Trump throughout 2017 and Kim more in 2018 - and has spent some of it to create a situation that brings North Korea and the U.S. to the table,” said Andray Abrahamian, adjunct fellow at the Griffith Asia Institute. “He’s still in a position to act as a go-between, but only as far as the other two parties take bridgeable positions.”

COMPLICATING FACTORS

The North’s outburst aimed at Moon’s government appeared partially driven by anger over South Korea allowing Thae Yong Ho, a former North Korean diplomat to Britain who defected to the South in 2016, to hold a press conference on Monday at the South Korean National Assembly for his publication of his memoir.

In his memoir, “Password from the Third Floor”, Thae describes North Korean leader Kim as “impatient, impulsive and violent”.

In rambling remarks in the White House’s Oval Office in which he also sharply criticized China over trade, Trump said that as far as he knew the meeting with Kim was still on track, but that the North Korean leader was possibly being influenced by Beijing after two recent visits he made there.

North Korea’s renewed ties with China “certainly has emboldened” Kim by making him less reliant on a successful summit with Trump, but Beijing is unlikely to be directing the latest outbursts, said Zhao Tong, a North Korea expert at the Carnegie-Tsinghua Center in Beijing.

“I am skeptical about the speculation that China was behind Kim Jong Un’s renewed hard line,” Zhao said. “I believe China wants North Korea and the U.S. to reach a deal, which would make it easier for China to enhance economic cooperation with North Korea and better facilitate North Korea’s strategic transition to economic development and open-up.”

“BRIDGE FOR SUCCESS”

Moon’s administration quickly accepted North Korean leader Kim Jong Un’s New Year’s proposal to ease tensions, arranged a historic inter-Korean summit, and passed on Kim’s invitation to meet with Trump.

North Korea, meanwhile, has pledged to publicly dismantle its nuclear test site next week.

South Korean officials said they still believe the nuclear site will be dismantled, and said they had not seen any changes in their lines of communication with the North Koreans.

Moon is scheduled to meet with Trump on Tuesday in Washington.

Despite professed unity, Trump has often taken a harder line on North Korea than Moon, and the U.S. president has repeatedly criticized South Korea over trade while questioning the usefulness of the alliance.

South Korea’s presidential Blue House, however, says it hopes Moon’s meeting with Trump will help set the stage for more progress with North Korea.

“As this U.S.-South Korea summit is taking place three weeks ahead of the U.S.-North Korea summit, we hope it will act as a bridge for the success of the U.S.-North Korea summit,” said Nam Gwan-pyo, second deputy director of the Blue House’s National Security Office.

(GRAPHIC: Nuclear North Korea - tmsnrt.rs/2lE5yjF)