South Korea's Moon Jae-in: Caught between Trump and Kim

Moon Jae-in is the man in the middle.

The South Korean president has become the mediator between Donald Trump and Kim Jong-un and is leading the diplomatic efforts to try to get North Korea to disarm.

Mr Moon's trip to Pyongyang on Tuesday, his third meeting with Mr Kim since April, may be his toughest challenge yet. He has to make real progress in persuading the North Koreans to make concrete steps to denuclearise. Otherwise the flurry of inter-Korean summits and the much-hyped Singapore meeting this year will be seen as glossy photo-ops, and President Trump may begin to lose patience.

With his approval rating dropping at home, Mr Moon needs a win. Here are some of the main obstacles he will need to overcome...

President Trump declared in June, after meeting Mr Kim, that there was no longer a nuclear threat from North Korea.

But many believe North Korea has no intention of giving up its "treasured sword". Having spent decades developing nuclear weapons, why would it dismantle them?

The only commitment Kim Jong-un has made so far has been a vague pledge to "denuclearise the Korean peninsula". It lacks detail. That is something President Moon needs to change.

"I think it's incredibly important that the North Koreans offer some sort of symbolically and substantively significant concession this week in order to keep the South Korean public interested," says Andray Abrahamian, from the Griffith Asia Institute.

"Giving Moon a win would bolster his position domestically and put pressure on the United States to keep moving forward.

"In a real sense, we might see the two Koreas co-operating to nudge the United States forward in the process."

South Koreans who talked to Kim Jong-un earlier this month said he was frustrated that his promise to denuclearise was not being taken seriously by the international community.

If Mr Kim is serious then this summit is a good time to put it in writing, as many fear Mr Moon and President Trump are being manipulated and Chairman Kim is playing for time.

Senator Lindsey Graham, of South Carolina, told CBS's Face the Nation on Sunday: "If they're playing Trump, we're going to be in a world of hurt, because he's going to have no options left. This is the last, best chance for peace right here."

The White House argues that Mr Kim's last missile tests were 10 months ago - and that in itself is a sign of progress. However, satellite images appear to show North Korea is continuing to work on building weapons.