South Korea's Yonhap news agency says senior DPRK official Kim Yong Chol is heading to the US, presumably for talks regarding the summit between Kim Jong Un and Donald Trump.

Kim Yong Chol was seen arriving at the Beijing Capital International Airport on Tuesday. He was at Kim Jong Un's side at the table in last weekend's North-South summit and was a prominent senior official in other important talks. Meanwhile, officials from the US and the DPRK are meeting again on the northern side of the inter-Korean border. Yonhap says this second session will likely focus on the details of a denuclearization deal. Our correspondent Nathan King has the story.

Progress in US diplomacy with the DPRK used to take years. Now it's measured in days.

After the two Korean leaders' second meeting in as many months.

A US negotiating team led by Sung Kim, a former US ambassador to South Korea - and former nuclear negotiator with the North - arrived in the DPRK for talks. The visit suggests the sort of advanced planning for a possible summit may now underway.

On Saturday, US President Trump expressed optimism.

DONALD TRUMP US PRESIDENT "A lot of people are working on it. It's moving along very nicely. So we're looking at June 12th in Singapore. That hasn't changed, and it's moving along pretty well. So, we'll see what happens."

Trump echoed that offer of economic assistance again on Sunday in a tweet saying in part:

"Our United States team has arrived in North Korea to make arrangements for the Summit between Kim Jong Un and myself. I truly believe North Korea has brilliant potential and will be a great economic and financial Nation one day. Kim Jong Un agrees with me on this. It will happen!"

At their Saturday summit, the two Korean leaders discussed the U.S. offer of economic assistance in return for denuclearization.

MOON JAE-IN SOUTH KOREAN PRESIDENT "I told Chairman Kim that if he decides and put into practice a complete denuclearization, President Trump is willing for economic cooperation and ending hostile relations."

But the DPRK hasn't budged on this proposal. Pyongyang says it's not ready to swap missiles for money. An article in the official workers party newspaper in Pyongyang said this on Sunday:

GVO Rodong Sinmun Newspaper "US media is still building up public opinion that the DPRK comes to the negotiating table with the US in a hope to get 'economic aid'."

The DRPK paper called the U.S. proposal "impudent" and "rubbish" adding:

"As far as the 'economic aid' is concerned, the DPRK has never expected it."

NATHAN KING WHITE HOUSE "So, both leaders from DPRK and the US appear to want this summit, but officials on both sides still have many details to work out - including when denuclearization will occur-before the summit as The White House has demanded or gradually, as Pyongyang has proposed. Nathan King, CGTN at the White House."