The joint excavation along the Demilitarised Zone of remains from the 1950-53 conflict was part of a military agreement signed at a Pyongyang summit in September between the South's President Moon Jae-in and the North's leader Kim Jong Un.

Under the deal -- aimed at defusing military tensions -- around 100 personnel from the two sides were to jointly carry out the recovery operation from April 1 to October 31.

But progress on the key issue of the North's nuclear weapons has since stalled, with Kim's Hanoi summit with US President Donald Trump breaking up in February without agreement, raising doubts over the future of inter-Korean projects.

Seoul's defence ministry said the North had not responded to its calls and the South Korean military would begin preparatory excavation work Monday on the southern side of the DMZ.

"We are making preparations so that it can be immediately shifted to a South-North joint excavation once North Korea responds," Roh Jae-cheon, the ministry's deputy spokesman, told reporters.

Moon -- who met Kim three times last year -- has long backed a policy of engagement with nuclear-armed, sanctions-hit Pyongyang and was instrumental in brokering talks between the US and North Korea.

At a meeting with his top aides on Monday, Moon said the failed US-North Korean summit in Vietnam posed a "temporary difficulty" but added: "It is clearly being confirmed that the South, the North, and the US all do not wish to go back to the past."

Moon, who will fly to Washington next week, said his rapidly arranged summit with the US president showed the allies wanted to revive the "momentum for dialogue at an early date".

Since Hanoi, Pyongyang and Washington have both sought to blame each other for the deadlock.

Pyongyang said it had proposed dismantling the Yongbyon complex -- a sprawling site covering multiple different facilities -- in exchange for the lifting of economic sanctions that have isolated the North.

But US officials have said the North wanted all significant sanctions removed while not making clear exactly which facilities at Yongbyon it was willing to give up -- and Trump has said that "the weapons themselves need to be on the table".