Prime Minister John Key says an international nuclear safety organisation is gaining greater access to Iran since a change in leadership there.
Mr Key has met with United Nations International Atomic Energy Agency director-general Yukiya Amano during the Nuclear Security Summit in the Hague.
Dismantling Iran's nuclear programme is one of the world's biggest diplomatic problems.
Mr Key says Mr Amano confirmed the Iranians have started curbing uranium enrichment.
"Since the change of leadership in Iran with President Rohani taking over they've really been getting a greater opportunity to assess what's been taking place in Iran and give a sense of how things are going. I mean, overall, the IAEA is a big organisation and we as a country contribute to that."
He says since President Hassan Rouhani was elected last June, the IAEA has been able to inspect Iran's nuclear activities and get a sense of what's happening there.
The situation in Iran has, meanwhile, been the focus of a protest near the Nuclear Security Summit.
More than a dozen people with flags and banners have been calling for the United States and the European Union to impose greater restrictions on Iran, after they were eased in January.
An organiser, Shahin Sultani Taien, says Iran is still very dangerous and it's right .that Iran is not invited to the summit.
He says nothing has changed in Iran.