The United States and North Korea will have frequent discussions until the goal of Pyongyang's denuclearization is reached, the State Department said Friday, declining to provide details on a reported meeting last weekend.

US Ambassador to Seoul Harry Harris is reported to have met with North Korean Vice Foreign Minister Choe Son-hui at the inter-Korean border village of Panmunjom Sunday to deliver a message from Washington.

The two sides have been in negotiations to implement an agreement reached by US President Donald Trump and North Korean leader Kim Jong-un at their historic summit in June.

The joint statement commits Kim to work toward the "complete denuclearization" of the Korean Peninsula in exchange for security guarantees from the US But progress has appeared slow as the two sides wrangle over who should take the first step.

Choe's counterpart in the substantive discussions has until now been US Ambassador to the Philippines Sung Kim, a North Korea expert.

The State Department refused to confirm that Harris was sent to Panmunjom.

"We don't have anything to share on this," a department spokesperson said in response to a Yonhap query. "Let me remind you that there will be many follow-up discussions until we reach our desired goal. Not all will be announced or read out."

The spokesperson added: "This is one of the most important national security challenges facing us today. It is not in our interest to share every detail of our negotiations."

US Secretary of State Mike Pompeo is rumored to be preparing for a fourth visit to Pyongyang in the coming days.

The top American diplomat said at a Cabinet meeting Thursday that he saw continued progress on North Korea and was "hoping that we can make a big step here before too long." (Yonhap)