UN spokesman Stephane Dujarric said Guterres considers the deal to be a "very important breakthrough to consolidate nuclear non-proliferation and advance global peace and security."
"The secretary-general very much hopes that it will remain in place," Dujarric added.
Trump is to unveil a more aggressive US strategy toward Iran that would stop short of withdrawing from the landmark accord but would declare that the deal is no longer in the US national interest.
The agreement, known as the Joint Comprehensive Plan of Action (JCPOA), was signed by Iran and six powers -- Britain, China, France, Germany, Russia and the United States -- under the previous administration of Barack Obama.
Trump's move could open the door to renewing US sanctions on Iran, a measure that diplomats say would lead to the collapse of the deal.
UN inspectors have said that Iran is complying with the agreement including its restrictions on uranium enrichment.
Guterres has repeatedly praised the JCPOA as a major diplomatic achievement and called for the agreement to be fully implemented.
The deal was enshrined in a Security Council resolution that was unanimously adopted in July 2015.
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![Ukrainian President, Volodymyr Zelensky and US President Joe Biden [BBC]](data:image/svg+xml;charset=utf8,%3Csvg%20xmlns%3D'http%3A%2F%2Fwww.w3.org%2F2000%2Fsvg'%20width%3D'300'%20height%3D'172'%20data-ring-placeholder%3D'1'%3E%3C%2Fsvg%3E "Ukrainian President, Volodymyr Zelensky and US President Joe Biden [BBC]")
