US Secretary of State Rex Tillerson has said that Iran is complying with a 2015 nuclear deal.

In a letter to House Speaker Paul Ryan, Tillerson certified that Iran was compliant through April 18 with its commitments under the 2015 Iran nuclear deal.

It was the first certification of Iran's compliance issued by President Donald Trump administration. Like his predecessor John Kerry, Tillerson is required to send the certification every 90 days.

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 US national security interests, NBC News reported.

Trump during his campaign repeatedly criticised the Iran nuclear deal, calling it "the worst deal ever negotiated".

Iran and six world powers — Britain, China, France, Germany, Russia and the US — reached an agreement on the country's nuclear issue in July 2015 that put Iran on the path of sanctions relief but with more strict limits on nuclear programme.

The deal set limits on Iran's nuclear activities as it would take Tehran at least one year to produce enough fissile material for producing a nuclear weapon, and allowed regular inspections of the facilities inside Iran.

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 sanctions drastically reduced crude oil exports from Iran. Since the sanctions have been lifted, oil exports from Iran to India have surged.

Iran was exempted from an OPEC deal to reduce output by 1.2 million barrels per day starting January 1, a victory for Tehran which argued it needs to regain the market share it lost during long years of sanctions.