The US State Department has said that Washington and Seoul are in close contact for a "unified response" to North Korea in relation to South Korea's plan to send a presidential envoy to Pyongyang, a US broadcaster reported Friday.

South Korean President Moon Jae-in told his US counterpart Donald Trump over the phone Thursday that he will soon dispatch a special envoy to the North. He expressed the intent while explaining the outcomes of recent visits by a special envoy and a high-level delegation from the North to the South on the occasion of the PyeongChang Winter Olympics.

"We are in close contact with the Republic of Korea about our unified response to North Korea, including the need to maintain maximum pressure to achieve a denuclearized Korean Peninsula," Radio Free Asia quoted Michael Cavey, a spokesman for the State Department's Bureau of East Asian and Pacific Affairs, as saying when asked about Moon's plan.

The spokesman stressed that the inter-Korean progress be accompanied by "advances" toward the North's denuclearization, the broadcaster said.

"We are willing to engage North Korea to emphasize our position that the complete and verifiable denuclearization of the Korean Peninsula is non-negotiable," the spokesman said.

Meanwhile, the White House made a similar response to the South Korean leader's plan.

"President Trump and President Moon noted their firm position that any dialogue with North Korea must be conducted with the explicit and unwavering goal of complete, verifiable and irreversible denuclearization," it said in a readout Thursday.(Yonhap)