"If foreign governments want to raise issues about the assumptions being made by journalists we will respond. We will do this in private rather than through the news media."
He won't say what the explanation was.
The Herald reported on Monday that Government Communications Security Bureau (GCSB) programmed an internet surveillance system to intercept emails about the candidates for the WTO post from Indonesia, Mexico, South Korea, Brazil, Kenya, Ghana, Jordan and Costa Rica in the period leading up to the May 2013 appointment.
New Zealand Trade Negotiations Minister Tim Groser was a rival candidate for the WTO job.
From an original field of nine, in mid April Mr Groser made it to the final five along with others from Indonesia, South Korea, Mexico and Brazil. The final two candidates were from Mexico and Brazil.
The Herald report was written by Nicky Hager and Ryan Gallagher of the US site The Intercept and was based on documents taken from United States spy agency NSA by Edward Snowden.
NSA and GCSB are sister organisations in the Five Eyes intelligence alliance of US, Britain, Canada, Australia and New Zealand.
The reports said that the GCSB used the XKeyscore system run by the NSA its WTO project.
Brazil reacted angrily in 2013 after reports, also based on Snowden documents, suggested that the NSA has listened to phone calls of the presidents of Brazil, Germany and Venezuela.
President Dilma Rouseff of Brazil cancelled a scheduled visit to Washington .
AFP has reported that US Vice-President Biden extended an invitation to her just last week for a visit this year- which would be the first in 20 years by a Brazilian president.