Seoul (AFP) - South Korea's new government will seek to sign a peace treaty with the North if it abandons its nuclear weapons, a minister said Thursday.

Vice Unification Minister Chun Hae-Sung's comments came hours before South Korea's new leader Moon Jae-In -- who backs engagement with Pyongyang -- was set to hold his first summit with US President Donald Trump, with the North's growing nuclear and missile threats casting a long shadow.

The two Koreas are still technically at war because a peace treaty was never agreed to replace the 1953 armistice that ended the conflict on the peninsula.

The US -- the South's security guarantor -- has 28,500 troops stationed in the country to protect it from its neighbour, and a treaty could entail their withdrawal, which has long been demanded by Pyongyang.

"We have to get over the current unstable system of armistice and put an end to the war on the Korean peninsula that has not yet ended," Chun said in a keynote speech at a seminar.

But a treaty could only be signed "at the stage of complete denuclearisation of the North", he added at the event organised by the Yonhap news agency.

The previous conservative governments of ousted president Park Geun-Hye and her predecessor Lee Myung-Bak shied away from referring to a peace treaty.

Signing a peace treaty with the United States used to be the North's standing demand in return for dismantling its nuclear programmes.

But it is unclear if Pyongyang still holds that view, with the isolated regime saying it will never give up nuclear weapons as it denounces the "hostile" US policy towards it.

On his plane to Washington, Moon told journalists Wednesday that the North should refrain from carrying out further tests and promise a nuclear freeze before dialogue could happen, while Seoul and Washington should consider what they could offer in return.

"A nuclear freeze is the entrance to dialogue and a complete dismantlement of nuclear programmes will be the exit of the dialogue," Moon was quoted as saying by news reports.

"Together with the nuclear dismantlement would come the establishment of a peace system on the Korean peninsula", Moon said, in an apparent reference to a treaty.