President of the Republic of Korea (ROK) Moon Jae-in said on Tuesday it was too early to be pessimistic about the stalled denuclearization dialogue between the United States and the Democratic People's Republic of Korea (DPRK), adding that Pyongyang has not yet shut the door to more talks. 

In his New Year's press conference at Cheong Wa Dae, Moon said, "I think we are not at the stage for now to be pessimistic about South-North dialogue and DPRK-U.S. dialogue, although it's not a stage to be optimistic."

If Pyongyang takes "substantive" denuclearization measures, the international community should take corresponding steps including sanctions relief, he added.

He also mentioned U.S. President Donald Trump's birthday greetings to DPRK's leader Kim Jong Un last week, which were sent in a personal letter.

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"(The) DPRK accepted it and immediately released a response. It stressed the relationship between the two leaders," the ROK president said.

Moon Jae-in also said the government was continuing to push for expanding inter-Korean cooperation with an "optimistic prospect".

The president also stressed China's efforts in denuclearizing the Korean Peninsula and building a permanent peace on the Peninsula, saying that China's role has been and will be very significant.

"Actually, China has provided an awful lot of help until now, and I am grateful (to China) for it," Moon noted.

ROK's top nuclear envoy will head to the U.S. this week for talks with his counterpart, according to ROK's Ministry of Foreign Affairs.

Lee Do-hoon, special representative for Korean Peninsula peace and security affairs, will leave for Washington on Wednesday and plans to meet with Deputy Secretary of State Stephen Biegun, who doubles as the chief U.S. envoy in negotiations with the DPRK.

On Saturday, the DPRK said the nuclear talks can resume only when the U.S. "fully accepts" Pyongyang's demands, and warned the ROK not to "meddle in" the relationship between Kim and Trump.

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Pyongyang's frustration has grown over the lack of progress in negotiating sanctions relief with Washington. 

Last month, Kim threatened the U.S. with a "Christmas gift" if concessions are not reached by the end-of-the-year deadline, days after his country announced it had successfully carried out another "crucial test" at the Sohae long-range rocket launch site.

Pyongyang is subject to multiple sets of international sanctions imposed over its nuclear and ballistic missile programs, and nuclear negotiations between the DPRK and the United States hit a stalemate since the second summit between Trump and Kim in Hanoi in February collapsed without a deal.  

The lifting some U.S. sanctions imposed on the DPRK was a key demand at the Hanoi summit.  

The latest working-level meeting between the two countries in October in Stockholm again broke down.

China calls for dialogue

In a move aimed at breaking the stalemate between Pyongyang and Washington, China and Russia proposed lifting some sanctions against the DPRK to the United Nations Security Council (UNSC) on December 17. 

Speaking in Beijing last month, Chinese Foreign Ministry spokesman Geng Shuang said the proposal was aimed at promoting the talks process and to "satisfy reasonable humanitarian and livelihood requirements" from the DPRK. 

"China hopes that the UN Security Council members take responsibility on the Peninsula issue, take active actions to support a political settlement, encourage dialogue and consultation, and maintain peace and stability on the peninsula," Geng said during a daily news briefing.

Geng also said that Beijing hoped to see Pyongyang and Washington meet each other halfway, while reaffirming China's commitment in supporting the denuclearization of the area.