A White House foreign policy advisor traveling with Vice President Mike Pence was quoted as telling reporters that the issue of completing the THAAD installation is up to South Korea's next president.

"As in any government decision, it may slip a couple of weeks or months. It's moving, but candidly until they get president... in the early part of May I think it's right so it should be a decision for the next president," the official said in the background on his way to Seoul.

The Ministry of National Defense, however, stressed the allies remain committed to the bilateral THAAD agreement signed last year.

"There is no change in the basic position of South Korea and the US to proceed, as planned, with preparations for the early operation of the THAAD system against North Korea's advancing nuclear and missile threats," the ministry's spokesman Moon Sang-gyun said at a press briefing.

Seoul and Washington are in the "final stage of consultations" over the provision of land before full-scale construction work, he added.

Moon indicated that its deployment won't be finished until South Korea's presidential polls.

South Korea has selected a golf course in Seongju, North Gyeongsang Province, as the site for the THAAD system. The defense authorities secured the land from Lotte Group in a property swap deal.

In March, the US military announced the "first elements" of the THAAD system have arrived in South Korea.

Those include two THAAD missile launchers known to be stored currently at a US Forces Korea base near Seongju.

It was not confirmed if the AN/TPY-2 radar, or X-band radar, which is a core element of the missile shield platform, is already in South Korea.

There have been political debates over whether South Korea should let the USFK position the missile defense system on its soil, which would severely damage its relations with China.

Moon Jae-in, the presidential candidate of the liberal Democratic Party, has called for a review of the matter by the next government.

Ahn Cheol-soo, the flag bearer of the center-left People's Party, said the Seoul-Washington deal should be respected from a diplomatic point of view. (Yonhap)