The body has called on Tehran to give access to two sites where past nuclear activity allegedly took place.
The board of governors at the United Nations' nuclear watchdog has passed a resolution critical of Iran, the first of its kind since 2012, as tension mounts over Tehran's nuclear programme.
Friday's resolution was put forward by European states and urges the Iranian government to provide inspectors from the Vienna-based International Atomic Energy Agency (IAEA) with access to two sites to clarify whether undeclared nuclear activity took place there in the early 2000s.
It "calls on Iran to fully cooperate with the Agency and satisfy the Agency's requests without any further delay, including by providing prompt access to the locations specified by the Agency".
Iran has been blocking access to the sites for months, prompting a growing diplomatic row.
The resolution was carried by 25 votes in favour versus two against, with seven abstentions: South Africa, India, Pakistan, Thailand, Mongolia, Azerbaijan and Niger.
Russia and China voted against.
The resolution was proposed by France, Germany and the United Kingdom, and supported by the United States - though the US ambassador to the UN in Vienna had said "the text could be strengthened".
'Iran categorically deplores this resolution'
Kazem Gharib Abadi, Iran's ambassador to the UN in Vienna, told Friday's meeting that the resolution will not "encourage Iran to grant access to the Agency based on fabricated and unfounded allegations".
"Iran categorically deplores this resolution and will take appropriate action in response, the repercussions of which would be upon the sponsors of this resolution," he added.
"While stressing the need for Tehran and IAEA to settle this problem without delay, we believe that the resolution can be counterproductive," Russia's Ambassador to the UN in Vienna Mikhail Ulyanov tweeted after the resolution was passed.