New Zealand's spy agency the Government Communications Security Bureau (GCSB) used the United States National Security Agency's (NSA) XKeyscore mass surveillance tool to spy on candidates from around the world vying to lead the World Trade Organisation (WTO).

GCSB used XKeyscore to set up searches for communications about candidates from Brazil, South Korea, Indonesia, Mexico, Ghana, Jordan, Kenya, and Costa Rica, according to a document released by NSA whistleblower Edward Snowden.

At the time in 2013, New Zealand's Minister of Trade Tim Groser was himself a candidate for the role.

The use of the tool for such a purpose appears to be far removed from the primary justification used by New Zealand Prime Minister John Key for GCSB's participation in the Five Eyes spy alliance; namely, fighting terrorism.

The government has refused to comment on the latest in a series of revelations about New Zealand's role in mass surveillance.

Glen Greenwald's website The Intercept is the main conduit for new Snowden releases. It has been working mainly with The New Zealand Herald in preparing and delivering the stories, which have also shone a light on New Zealand's role in filling a South Pacific gap in the NSA's global reach.

New Zealand's GCSB collects communications from many small Pacific nations, and also from certain Asian nations to help complete the Five Eyes' surveillance dragnet.

Of particular interest in the WTO surveillance was Indonesia's candidate, former Trade Minister Mari Pangestu.

South Korea's candidate Dr Taeho Bark was also among those targeted. New Zealand is scheduled to sign a free trade agreement with South Korea on Monday.