Prime Minister Bill English does not expect reports that New Zealand spied on Japan during whaling talks will affect any future visits to the country, he says.
The Intercept website has published a National Security Agency (NSA) document, received from US whistleblower Edward Snowden, as part of an article on Japan's secretive relationship with the US agency.
The document, marked top secret, outlined a mission where Government Communications Security Bureau (GCSB) spies collected information on Japan and passed it on to the US ahead of a key vote at an international whaling meeting in 2007.
Mr English said he would not comment on any specifics, and would only say the GCSB must follow the law.
"That law has just been overhauled quite significantly with the support of the overwhelming majority of the parliament. And we would expect them to continue to comply with the law."
Mr English said Japan has not demanded that New Zealand explain itself.
The Japanese embassy said today it was not in a position to comment.
New Zealand spies collected 'insightful' intelligence
US whistleblower Edward Snowden. Photo: RNZ
Japan had been lobbying countries to support pro-whaling proposals at a four-day International Whaling Commission (IWC) gathering at Anchorage, Alaska, the article said.
The US did not want such measures to pass, but negotiations were "really coming down to the wire" and the outcome was "uncertain".
New Zealand spies were collecting "insightful" intelligence that "laid out the lobbying efforts of the Japanese and the response of countries whose votes were so coveted", the document said.
"US officials were anxious to receive the latest information during the actual negotiations in Anchorage."
As such, the paper said, every morning, an NSA operative would take a half-hour taxi ride from the function to the agency's Alaskan Mission Operations Center.
The staffer would collect printed copies of the GCSB intelligence and then take them in a locked bag to a private conference room.
There, four US officials, two New Zealand delegates and one Australian would study the information, "pointing and nodding" as they did so, the document said.
"We knew the delegates valued the material simply because they took time from their very hectic schedules to be there and read it."
On the forum's final day, Japan ditched its proposal that some of its villages be allowed to hunt whales for commercial purposes, when it became apparent it did not have enough support.
Japan threatened to quit the commission altogether.
The NSA document did not reveal the contents of the intelligence, but concluded the outcome was worth the effort.
"The Australian, New Zealand, and American delegates would all say 'yes'. I believe the whales would concur," it finished.
The GCSB could not be reached for comment last night.
Sir Geoffrey Palmer, who was appointed New Zealand's representative on the IWC in 2002, denied any knowledge of the events outlined in the NSA documents.
In 2015, New Zealand journalist Nicky Hager accused the GCSB of spying on New Zealand's Pacific neighbours and passing that information on to the US.
He also alleged the spy agency monitored Japan, China, India, Pakistan, Iran, countries in South America and even isolated scientific bases in Antarctica.
Mr Hager said New Zealand was helping the NSA to fill in gaps in its global surveillance in order to win brownie points in Washington.
Meanwhile, intelligence leaders from the US, the UK, Canada, Australia and New Zealand are in Arrowtown this week for an annual meeting of the Five Eyes alliance.
FBI director James Comey and CIA director Mike Pompeo are among those understood to be at the event.
The minister responsible for the SIS and GCSB, Chris Finlayson, is also attending and Prime Minister Bill English was to join a dinner at the conference last night.