Foreign Affairs Minister Murray McCully has met United States Secretary of State Hillary Clinton for the first time at meeting in Washington.
Mr McCully says Mrs Clinton described the relationship between the two countries as the best it has been for 25 years.
US President Barack Obama this week announced his intention to work towards a world free of nuclear weapons.
Mr McCully says he signed a document at Wednesday morning's meeting to confirm New Zealand's support for the G8 Global Partnership Against the Spread of Weapons of Mass Destruction.
He says the agreement involves helping the US to stop the trafficking of nuclear material around the borders of Kazakhstan.