South Korea's top nuclear envoy left for the United States on Tuesday for talks with his counterpart amid growing hopes for a restart of denuclearization talks between Washington and Pyongyang.

During his four-day trip to Washington, Lee Do-hoon, special representative for Korean Peninsula peace and security affairs, is scheduled to meet US Special Representative for North Korea Stephen Biegun, the foreign ministry said. 

"I believe various forms of contact are being made (between the North and US). I can tell you that we're going in the direction where we can revive the momentum for dialogue," he told reporters at Incheon International Airport, west of Seoul.

"We are at a point in time where the resumption of talks between the North and the US is needed more than ever. We share that understanding and we will do our best to get the talks restarted by putting together all diplomatic efforts possible," he said.

Lee's meeting with Biegun is expected to take place on Wednesday (Seoul time).

They are expected to exchange views on the situation on the Korean Peninsula and discuss ways to cooperate on facilitating a swift resumption of the US-North Korea dialogue for the complete denuclearization of the North.

The meeting of the two nuclear envoys also comes ahead of a series of major diplomatic events set to happen in the coming days.

Chinese President Xi Jinping is due to make his first visit as president to North Korea on Thursday. US President Donald Trump is coming to Seoul after attending a Group of 20 summit that will take place in Osaka on June 28 and 29. 

"June will be a very important month for (South Korean) diplomacy," Lee added. 

The denuclearization talks have hit an impasse after the Hanoi summit between Trump and North Korean leader Kim Jong-un ended without a deal. They failed to agree on the scope of the North's denuclearization and sanctions relief by Washington. 

Hopes for resuming the talks were rekindled last week when Trump said he received a "beautiful and warm" letter from Kim. In an interview with ABC News on Sunday, Trump said his relationship with Kim remains "very good" and "strong."  

The two envoys are scheduled to make keynote speeches at the Atlantic Council-East Asia Foundation Strategic Dialogue, the first time they will have appeared on a stage together at a private event. 

During his stay in Washington, Lee is also expected to meet officials from the State Department and the National Security Council. (Yonhap)