"The nuclear deal doesn't belong to one country, it belongs to the international community," Mogherini told a news conference alongside Russian Foreign Minister Sergei Lavrov, according to Reuters on Tuesday.
"We have the responsibility to make sure that this continues to be implemented,” she added.
The administration of US President Donald Trump said in April it was launching an inter-agency review of whether the lifting of sanctions against Iran was in the United States' national security interests.
Iran and the Group 5+1 (Russia, China, the US, Britain, France and Germany) reached the 159-page nuclear agreement, also known the Joint Comprehensive Plan of Action (JCPOA), in July 2015 and implemented it in January 2016.