The ongoing deployment of a US missile defence system in South Korea is a self-defence measure aimed solely at North Korea's nuclear and missile threats, South Korea's Yonhap news agency reported a senior foreign ministry official as saying Wednesday.

South Korea and the US recently started the process of installing a Terminal High Altitude Area Defence (THAAD) system.

They said that it is aimed at better coping with the North's missile threats, but China has voiced strong objection claiming that the shield equipped with a strong radar could be used against its military.

China has been stepping up its retaliation against South Korea mostly in the business, culture and tourism sectors.

Beijing's ban on sales of tour packages to South Korea that went into effect on Wednesday is seen as the latest in a string of retaliatory actions.

"Deploying THAAD is a measure taken to cope with the North's nuclear and missile threats," Vice Foreign Minister Ahn Chong-ghee told lawmakers during a parliamentary committee meeting on foreign affairs.

"We will respond to China with dignity on this self-defence decision."

With regard to possible countermeasures, Ahn said that the ongoing retaliation, including the ban on trips to Korea, could be in violation of the World Trade Organisation treaties in the service sector if the government's involvement is proven.

He, however, admitted that circumstantial evidence only is not enough to prove the illegality at a time when the Chinese government is denying any involvement.

"China does not acknowledge government involvement in these measures, but the overall situation points to Chinese government involvement," Ahn said.

"There were similar cases in the past, including restrictions on travel, where China put pressure on countries like Norway, Japan and the Philippines during diplomatic disputes."

The vice minister said that the government is still making it clear to Beijing that South Korea is in strong need of THAAD to guard itself against outside threats and that there is no need for it if the North gives up its nuclear program.

"The government believes China is stepping up its pressure in stages as the THAAD placement progresses, and we expect it to have a considerable impact on our business activities and people-to-people exchanges," he said.

"In the medium to long term, we plan to reduce our reliance on China." --Bernama