However, calling Iran "a leading state sponsor of terror", Tillerson informed Congress that the Trump administration had directed a full review of the 2015 nuclear deal to evaluate whether continued sanctions relief was in the U.S. national security interests, NBC News reported.
Under the 2015 Joint Comprehensive Plan of Action, the USA and five other powers agreed to lift some sanctions on Iran if the country would restrict its nuclear activities.
But in a statement, Mr Tillerson said: "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.is vital to the national security interests of the United States".
The certification was the latest signal that US President Donald Trump, who campaigned against the Iran deal and at times suggested he would scrap it, has as president adopted a more toned-down posture related to the Iranian regime.
Yet the US Department of State maintained that an interagency review of the Iran deal was being conducted due to concerns regarding the Islamic Republic's continued role as a state sponsor of terrorism.
"Iran remains a leading state sponsor of terror, through many platforms and methods", wrote Tillerson.
Tillerson said the 2015 nuclear deal between Iran and six world powers failed "to achieve the objective of a non-nuclear Iran and only delays their goal of becoming a nuclear state".
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He did not say how long the review would take but said in the letter to Ryan that the administration looked forward to working with Congress on the issue.
Tillerson said Iran has complied with the agreement's terms through Tuesday, the day he released the letter.
The certification of Iran's compliance, which must be sent to Congress every 90 days, is the first issued by the Trump administration.
On Monday, Foreign Policy reported that the Trump administration was considering increasing current United States sanctions against Iran. If not, Trump will place the U.S.in violation of its commitments and be responsible for unilaterally killing the nuclear deal.
The White House, however, has ordered a full review of the agreement.
As CNN notes, if the USA were to reapply sanctions against Iran, it would go against the terms of the JCPOA.