SYDNEY (AFP) - A South Korean spy ring has been uncovered in Australia trying to cultivate public servants to obtain trade secrets, a report said on Thursday.

The Sydney Morning Herald said previously suppressed information revealed that South Korea's National Intelligence Service (NIS) had sought "to obtain sensitive information" on trade negotiations between Canberra and Seoul.

The Herald reported that the Australian Security Intelligence Organisation (ASIO) alleged that a senior Australian agricultural trade specialist was involved in "foreign interference" by the Korean spies and had been "successfully cultivated".

The man, named by the newspaper, participated in Australia-South Korea free trade agreement talks in late 2009 but lost his security clearance and job with the Australian Bureau of Agricultural and Resource Economics and Sciences.

Although engaged in what ASIO described as "inappropriate activities" harmful to Australia's interests, no South Korean spies had been expelled from Australia.

Instead, in an effort to maintain good relations with the NIS, ASIO took legal action to prevent disclosure of the incident and protect the identities of the South Korean agents.

The details came to light after the trade specialist said his contact with South Korean diplomats was purely social and appealed against his sacking to the Federal Court.

In releasing information about the case, the court identified four NIS officers who served under diplomatic cover in Canberra.

A spokesman for Foreign Minister Bob Carr declined to comment on the case.

"It is the longstanding practice of successive governments not to comment on actual or alleged intelligence matters," she said.

South Korea is one of Australia's largest export markets and trading partners.