(CNN) A top official at North Korea's Foreign Ministry has accused South Korean President Moon Jae-in of lying about back channel talks between Pyongyang and Washington in order to manipulate public opinion, complicating efforts by Seoul to revive nuclear negotiations between the two sides.

The comments, published in North Korea's state-run news outlet KCNA Thursday, come a day after Moon said officials from Pyongyang had been talking "behind the scenes" and "engaged in dialogue in regard to a third summit."

Moon's supposed revelation and a recent exchange of letters between North Korean leader Kim Jong Un and United States President Donald Trump had led to suggestions that the two sides could revive stalled denuclearization talks during Trump's trip to Asia beginning Thursday.

Negotiations have, at least publicly, seemed to be stuck in neutral since the February summit between Trump and Kim in Hanoi ended abruptly and without an agreement.

The US Special Representative to North Korea, Stephen Biegun, said earlier this month that "the door is wide open" for talks to continue, but noted that "US-North Korean diplomacy has been in something of a holding pattern" since Hanoi.

In the statement published Thursday, Kwon Jong Gun, the director general of the Department of American Affairs at North Korea's Foreign Ministry, denied Moon's assertion that behind-the-scenes dialogue was taking place between and accused South Korea "trying to refurbish their image" by acting publicly as "if they are 'mediating.'"

Since taking office in 2017, Moon has essentially positioned himself as mediator between the United States, a treaty ally of South Korea, and North Korea. But Kwon said that the recent detente between the two countries was due to the "personal relations between Comrade Chairman of the State Affairs Commission and the US President," referring to Trump and Kim.

"If we have anything to liaise with the US, it will be simply done through the liaison channel already under operation between the DPRK and the US, and the negotiation, if any, will be held face to face between the DPRK and the US," Kwon said.

"There will be no such a happening where anything will go through the South Korean authorities."

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'A different forum'

Trump is due to arrive in Osaka Thursday evening local time for the two day meeting of international leaders, before traveling to Seoul to meet with with Moon Sunday.

Trump said Wednesday that he may speak with Kim on his trip to Asia "in a different forum," but declined to specify what that would entail.

"I'll be meeting with a lot of other people, not by him, but I may be speaking to him in a different forum. I'll be going, as you know, to South Korea after we're finished with the G20 and we'll be there for about a day. We have a lot of meetings planned with a lot of different countries," Trump said ahead of his departure.

But a US source familiar with the discussion between the three countries said Wednesday that Washington isn't holding its breath for forward movement during Trump's visit to South Korea, and accused Seoul of trying to talk up the potential of a third summit.

The source also echoed some of the criticism from North Korea's Kwon, saying there are no specific plans for laying the groundwork for a future summit with Kim during Trump's trip to Seoul.

Experts have also stressed the lack of preparation.

"Two improvised, unprepared summits have failed to produce a significant arms control deal. Today, we are even further from the necessary conditions for success than we were then. Working level negotiations and the South Korean peace process have both ground to a halt," said Adam Mount, the director of the Defense Posture Project at the Federation of American Scientists.

"Kim Jong Un is no more ready to eliminate his nuclear arsenal now than he was a year ago. If the Trump administration is finally ready to craft an achievable agreement that starts with a verifiable nuclear and missile test freeze, it could make for a real win. But it requires a shift in strategy and serious preparation."

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Vipin Narang, a professor at MIT who specializes in nuclear proliferation and strategy, said it appears unlikely a summit is forthcoming.

"My expectations are low, and I think going forward it's best to keep them there" he said, adding that it's more likely that developments will come from meetings between senior officials.

Regarding the "different forum" Trump referred to, Narang said it's possible Trump and Kim speak on the phone.

"The fundamentals are whether the US and North Korea are willing to walk down from their maximalist positions and there is no indication either have," Narang said.

"And with each passing day it gets harder for them to do so without risking domestic hardliner backlash."

Kwon's comments published in KCNA also said the United States needs to consider a "realistic proposal" before North Korea returns to he table.

He also reiterated comments Kim made in an important policy speech in April , saying that the US needs to change its negotiating strategy by the end of the year or North Korea would be forced to reassess the value of negotiations.

"Even though we are to think of holding a dialogue with the US, we need first to see a proper approach towards the negotiation on the part of the US," Kwon said.

"The US would be well advised to bear in mind that our repeated warning is not merely an empty word," he said.

Those comments echoed rhetoric warning from a North Korean Foreign Ministry spokesman Wednesday , which accused Washington of "hostility" and "viciously" slandering Pyongyang.

That statement was careful to spare Trump from the criticism, instead directing it at his aides.