North Korea has yet to offer any substantive response to requests from United Nations Command to confirm the safety of a US service member in its custody, a state department spokesperson said Wednesday.

In addition, Pyongyang remains unresponsive to such requests from the United States, according to the department spokesperson, Matthew Miller.

His remark comes after a Department of Defense spokesperson said the North has responded to UNC requests to confirm the whereabouts of Pvt. Travis King, who crossed the inter-Korean border into North Korea last week.

"It was my understanding ... that it was a call to the UN Command at the demilitarized zone that came just in the last 48 hours," Miller told a daily press briefing.

"It was not a substantive call. It was an acknowledgment call," he added. "That wasn't substantive and so because it wasn't substantive, we certainly don't see it as progress."

Shortly after the US soldier crossed into North Korea last week, the state department spokesperson said the US had a "number of diplomatic channels" through which it can communicate with North Korea.

"The outreach that we have made to North Korea through diplomatic channels has still not been answered," Miller told the press briefing.

When asked about North Korea's withdrawal from the Nuclear Nonproliferation Treaty 20 years ago in 2003, the state department spokesperson called on Pyongyang to stop its "continued pursuit of ballistic missile technology and nuclear weapons."

"As we have made clear from the outset of this administration, we are open to conversations, we would welcome conversations with North Korea about these issues, and they have refused to engage meaningfully with us," said Miller. (Yonhap)