North Korea on Thursday threatened to stall progress of the Korean Peninsula's denuclearization as it accused the United States of pushing for international sanctions and making baseless allegations despite Pyongyang’s goodwill moves.

"As long as the U.S. denies even the basic decorum for its dialogue partner and clings to the outdated acting script which the previous administrations have all tried and failed, one cannot expect any progress in the implementation,” a North Korean foreign ministry spokesperson said in a statement.

It accused U.S. of “making baseless allegations against us and making desperate attempts at intensifying the international sanctions and pressure” and "insulting the dialogue partner and throwing cold water over our sincere efforts for building confidence which can be seen as a precondition for implementing” the agreement between North Korean leader Kim Jong Un and Trump.

"The U.S. should, even at this belated time, respond to our sincere efforts in a corresponding manner," the statement said, adding it was still willing to implement the agreement made at the June 12 summit. "As long as the U.S. denies even the basic decorum for its dialogue partner... one cannot expect any progress in the implementation of the DPRK-US joint statement including the denuclearization ... both sides should make efforts to settle the problems."

“Since we know that the U.S. will never give up its hostile policy toward us, we will hold on to our nuclear knowledge,” North Korea’s foreign minister, Ri Yong Ho said, the Guardian reported.

These statements came days after a confidential United Nations report, which was leaked last week, revealed North Korea has "not stopped its nuclear and missile programs" and was evading sanctions through ship-to-ship oil transfers.

Following the leak, several U.S. officials this week expressed their frustration over North Korea's behavior and stressed the need for Pyongyang to take additional steps toward denuclearization.

Reacting to the leak, U.S. ambassador to the United Nations Nikki Haley said Wednesday, "They have to understand that the international community still expects them to denuclearize and so we're willing to wait if they want to wait, but we're not willing to wait for too long." 

U.S. State Department spokeswoman Heather Nauert said Thursday the two nations are in direct communication "virtually every day.”

"I can tell you we continue to have conversations virtually every day, every other day or so with the North Koreans. When I say 'conversations,' that can be by phone, that can be my message, that can be by email. We continue to have conversations with the government," Nauert said.

On Tuesday, Trump’s national security adviser John Bolton accused North Korea of not taking necessary steps to denuclearize and said the president is willing to meet Kim anytime.

NK - US North Korea threatened to stall progress on the denuclearization of the Korean Peninsula as it accused the U.S. of pushing for international sanctions and making baseless allegations despite Pyongyang’s goodwill moves. In this image, President Donald Trump and North Korea's leader Kim Jong Un shake hands during the signing of a document after their summit at the Capella Hotel on Sentosa island in Singapore, June 12, 2018. Photo: Susan Walsh/Pool via Reuters/File Photo

Satellite images from June 21 showed Pyongyang upgrading the infrastructure including construction of a new cooling water pump and new buildings at its only nuclear research facility used to fuel its weapon programs.

According to the study, staining was noticed of the cascade halls by deposition of water vapor, which meant the uranium enrichment plant is operational.