Seoul, May 30 (IANS): South Korean President Moon Jae-in on Tuesday ordered a thorough investigation into the unauthorised delivery of four more mobile launchers of the US missile shield to the country.

Yoon Young-chan, chief Presidential Press Secretary, told the media that Moon said it was "very shocking" after he was briefed on the unauthorised transportation, Xinhua news agency reported.

Top presidential security advisor Chung Eui-yong reported to Moon that four more THAAD mobile launchers were secretly transported to South Korea in addition to two launchers already installed.

Moon ordered the security advisor and the senior presidential secretary for civil affairs to thoroughly look into the secret delivery.

About two weeks before the May 9 presidential election, two mobile launchers and a radar for the US Terminal High Altitude Area Defence (THAAD) missile interception system were transported in the night to a golf course at Soseong-ri village in North Gyeongsang province.

THAAD is composed of six mobile launchers, 48 interceptors, an AN/TPY-2 radar and a fire and control unit.

The clandestine transportation raised speculation that it was aimed to politicise security issues during the election campaign period, which tended to benefit conservative candidates in past elections.

Moon earlier on Tuesday called Defence Minister Han Min-koo, who was appointed by ousted President Park Geun-hye, to verify the secret delivery of four more launchers, according to the presidential Blue House.