The Chung-McMaster meeting was held in San Francisco over the weekend. The two-day meeting also involved their Japanese counterpart, Shotaro Yachi, officials from the South Korean presidential office Cheong Wa Dae said earlier.

"The three countries agreed to work closely together for the success of the South-North summit that will be held in late April and the US-North Korea summit to be held shortly thereafter," Chung said.

Chung's latest US trip marked the second of its kind following his rare visit to the communist North as Moon's special envoy on March 5-6.

It was his trip that helped arrange the upcoming summits among the leaders of South Korea, the US and North Korea.

The inter-Korean summit, if held, will mark the third of its kind, but the first to be held on South Korean soil as it is set to be held on the South Korean side of the joint security area, also known as Panmunjom, inside the heavily fortified Demilitarized Zone.

The proposed US-North Korea summit will mark the first of its kind in history. US President Donald Trump has said he will meet the North Korean leader before the end of May. (Yonhap)