In a letter to US House of Representatives Speaker Paul Ryan, the top Republican in Congress, on Tuesday Tillerson said Iran remained compliant with the 2015 deal.
Under the deal, the State Department must notify Congress every 90 days on Iran's compliance under the JCPOA. It is the first such notification under US President Donald Trump.
"The US Department of State certified to US House Speaker Paul Ryan today that Iran is compliant through April 18 with its commitments under the Joint Comprehensive Plan of Action," Tillerson said in a statement, Reuters reported.
"President Donald J. Trump has directed a National Security Council-led interagency review of the Joint Comprehensive Plan of Action that will evaluate whether suspension of sanctions related to Iran pursuant to the JCPOA is vital to the national security interests of the United States," Tillerson added.
Tehran and the Group 5+1 (Russia, China, the US, Britain, France, and Germany) reached the nuclear deal on July 14, 2015 and started implementing it on January 16, 2016.
The comprehensive nuclear deal terminated all nuclear-related sanctions imposed on Iran.