An American embassy representative says United States Secretary of State Condoleezza Rice's use of the word ally to describe New Zealand was "deliberate and thought about" and reflects existing co-operation.
Dr Rice was in Auckland on Saturday for top-level talks, including meetings with Prime Minister Helen Clark and Foreign Affairs Minister Winston Peters.
She described New Zealand as a friend and an ally following her meeting with Miss Clark at Government House.
The reference to New Zealand as an ally was one of the strongest public statements of support for Wellington since relations between the two countries were ruptured in the mid-1980s by New Zealand's anti-nuclear policy.
US Embassy Charge d'Affaires, David Keegan, told Morning Report the terminology reflects the new level of co-operation between New Zealand and the United States in recent years.
Mr Keegan says when a secretary of state speaks publicly, it can be assumed that the language is well considered. "I think what's important about that word ally is that it reflects what we've been doing over the past couple of years. Its a recognition that we've been co-operating on a lot of different issues and a lot of different places, very deliberately."
A senior fellow at Victoria University's Centre for Strategic Studies, Terence O'Brien, says Dr Rice's visit shows the US has discovered it needs friends and allies because of the problems created by the present administration's foreign policies.
He says the term ally does not mean military ally, and joint military exercises would still require a presidential waiver because of New Zealand's nuclear free status.
Mr O'Brien, who is also a former diplomat, says being a military ally of the US would mean coming under the American nuclear umbrella.
He says the relationship between the two countries has been gradually improving, partly because of New Zealand's role in Afghanistan. But being a military ally implies some sort of written agreement, and it is too early to know whether either country would want to formalise the relationship in that way.