After the International Atomic Energy Agency verified in January of 2016 that Iran was in compliance with terms to scale back its nuclear programme, some international sanctions were lifted.
The State Department told Congress on Tuesday that Iran has so far complied with the 2015 nuclear deal - and President Trump has ordered a review of the sanctions lifted against the country under the deal. It added: "When the interagency review is completed, the administration looks forward to working with Congress on this issue".
Despite the sanctions relief, Iran remains on the State Department's list of state sponsors of terrorism for its support of anti-Israel groups and is still subject to non-nuclear sanctions, including for human rights abuses and for its backing of Syrian President Bashar Assad's government.
However, in a letter sent late Tuesday to House Speaker Paul Ryan, Secretary of State Rex Tillerson said the administration has undertaken a full review of the agreement, known as the Joint Comprehensive Plan of Action.
The nuclear deal was struck in July 2015 after 18 months of negotiations between the U.S., U.K., China, France and Russia, Germany, and Iran.
Last month Trump's Defense Secretary James Mattis said Iran continued to behave as an exporter of terrorism and still sponsors militant activity. Tillerson's letter is the first notification under the Trump administration.
Though there was no sign the Trump administration meant to walk away from the deal, Tillerson twice cautioned that if left unchecked Tehran could become a threat like North Korea, which is also under pressure over its nuclear ambitions.
Iran has yet to comment on the Trump administration's review, but Iranian Supreme Leader Ayatollah Khamenei warned in November that Tehran would retaliate if the United States breached the nuclear agreement.
The European Union's foreign policy chief, Frederica Mogherini, said last month after meetings with senior Trump administration officials she was reassured in the talks that the U.S. was committed to fully implementing the deal.
Reapplying sanctions would violate the terms of the groundbreaking deal signed with Iran by former President Barack Obama, Russia, China and European Union partners.