WASHINGTON -- US President Donald Trump received a letter from North Korean leader Kim Jong-un this week, the White House said Thursday, in the latest sign of top-level diplomacy on Pyongyang's denuclearization.

"A letter to President Trump from Chairman Kim was received on August 1," White House press secretary Sarah Sanders said in a statement. "The ongoing correspondence between the two leaders is aimed at following up on their meeting in Singapore and advancing the commitments made in the US-DPRK joint statement."
 

Sanders did not provide details on the content of the message.

Trump mentioned the letter in a tweet earlier Thursday as he thanked Kim for returning the remains of presumed American soldiers killed in the 1950-53 Korean War.

Fifty-five cases of remains were airlifted from North Korea to South Korea last week and honored in a solemn ceremony at Joint Base Pearl Harbor-Hickam in Hawaii Wednesday.

The repatriation was part of an agreement Trump and Kim reached at their historic summit in Singapore in June.

"Thank you to Chairman Kim Jong Un for keeping your word & starting the process of sending home the remains of our great and beloved missing fallen!" Trump wrote in the tweet. "I am not at all surprised that you took this kind action. Also, thank you for your nice letter -- l look forward to seeing you soon!"

Sanders later told reporters that there are currently no plans for a second summit.

"Certainly open to that discussion, but there isn't a meeting planned," she said at a regular press briefing, adding that Trump has written a reply to Kim's letter.

"That letter will be delivered shortly," she said. "I can say that the letters addressed their commitment from their joint statement that was made at the Singapore summit and they're going to continue working together towards complete and total denuclearization."

While it is hoped that the repatriation will give momentum to the implementation of the key element of the deal -- the dismantlement of North Korea's nuclear weapons program -- progress toward securing firm commitments in that regard from Pyongyang has reportedly been slow.

The Washington Post, citing officials familiar with US intelligence, reported this week that North Korea appears to be building up to two liquid-fueled intercontinental ballistic missiles.

Meanwhile, 38 North, a US website monitoring the regime, said last month that satellite imagery pointed to the dismantlement of a missile engine testing site in line with Kim's verbal promise to Trump at the summit.

Last Friday -- the day North Korea returned the remains -- coincided with the anniversary of the signing of the Armistice Agreement, which ended fighting in the war. Pyongyang has called for a formal declaration to end the war, viewing it as a guarantee of its security in exchange for denuclearization.

At the summit, Trump committed to provide security guarantees to the regime.

He also declared shortly after the meeting that North Korea's nuclear threat was now over, inviting backlash from critics who slammed the joint statement as lacking in substance.

Trump has maintained his optimism about North Korea's denuclearization, while saying there is no time limit on the negotiations.

In July, he revealed the full contents of another letter from Kim on Twitter.

The message expressed hope for the opening of a new future between the countries as agreed to during the summit. (Yonhap)