WASHINGTON -- The United States will continue to work closely with its allies and partners, including China and Russia, to denuclearize North Korea, US National Security Adviser Jake Sullivan said Monday.

The White House adviser also said the North continues to remain unresponsive to US overtures for dialogue.

"We have not yet heard directly from them through diplomatic channels," he said in an interview with MSNBC.

The US earlier said it has reached out to North Korea through "multiple" diplomatic channels since mid-February.

"But, as we have indicated, we have reached out because we believe that diplomacy has to be part of the process of getting to a denuclearized North Korea. And we remain intent on achieving that goal," said Sullivan.

North Korea has reached out to the US in what South Korea's Foreign Minister Chung Eui-yong has called its own way of sending a message.

In a statement delivered by North Korea's state news outlets last week, First Vice Foreign Minister Choe Son-hui warned that US had better refrain from causing a stink if it wishes to sleep in peace for the next four years.

Sullivan said the US will continue working with US allies and partners to bring North Korea back to the denuclearization talks.

"And we also want to make sure that we are pulling together with our allies, Japan and South Korea, and engaging other regional actors, including China and Russia, in a process that shows that this is ultimately up to North Korea to come forward and act in a constructive manner," he said.

"In the meantime, the US will continue to stand up firmly on behalf of our own defense and the defense of our allies and partners."

North Korea has stayed away from the negotiating table since the second US-North Korea summit between Donald Trump and Kim Jong-un ended without a deal in Hanoi in February 2019.

The first-ever US-North Korea summit was held between the former US president and Kim in Singapore in June 2018. (Yonhap)