South Korean hopes for a breakthrough in the nuclear impasse on the peninsula were hit by a double whammy after the United States re-listed Pyongyang as a state sponsor of terror and North Korean leader Kim Jong Un appeared to have snubbed a special Chinese envoy.

Expectations were high that Mr Song Tao, who flew to Pyongyang last Friday to brief the North Korean regime on China's recently ended national congress, would also deliver a message to Mr Kim to resume talks on the nuclear issue.

At least one top analyst here saw the snub as implying that North Korea was "not happy with what China is demanding".

"Therefore, it could be a bad signal to the peaceful resolution of the North Korean issue," said Yonsei University's Professor Moon Chung In, a special adviser for foreign affairs and national security to South Korean President Moon Jae In.

Prospects for dialogue may not be so bright now, especially with the US preparing to impose even more sanctions on the North.

But the setbacks are unlikely to sway President Moon's long-term goal of improving ties with the North, nor put the brakes on the baby steps taken by his administration to reach out to Pyongyang.

In September, the South Korean leader approved a US$8 million (S$10.8 million) humanitarian aid package for North Korea, and on Monday, permission was granted to a South Korean man to travel across the border to visit the grave of his mother who defected to the North with his father in the 1980s. He is due to embark on the journey today.

Prof Moon said Pyongyang's nuclear and missile tests as well as its refusal to return to talks made it "inevitable" for Seoul to adopt the US-led sanctions policy, even though the South Korean President had made dialogue with the North a top priority.

"Sanctions are the means to induce North Korea to come out to the negotiating table... If North Korea cooperates, we can move towards dialogue," said Prof Moon.

Pyongyang's lack of provocative action in the past two months - its last missile test was on Sept 15 - had been widely interpreted as a window of opportunity for negotiations to take place.

Some analysts remain hopeful, believing it to be too early to write off Chinese mediation efforts.

Sejong Institute research fellow Lee Seong Hyon said: "China and North Korea are like estranged lovers who haven't talked to each other for a while.

"So, they need some practice and a couple more warming-up chats to get back on the normal track."