The agency's comments come against the backdrop of the United States tightening its sanctions on leading oil producer Iran.
"Further tightening of sanctions on Iran will have an impact on its export capacity," the Paris-based IEA said, adding Iranian shipments of crude and condensates are running around 1.1 million barrels per day (bpd), 300,000 bpd lower than March, and 1.7 million bpd lower than May 2018.
The agency, which coordinates the energy policies of industrialised nations, said global spare production capacity has risen to 3.3 million bpd due to high compliance rate with the agreed supply cuts among the Organization of the Petroleum Exporting Countries and its allies.
OECD oil inventories at the end-February were at 2.871 billion barrels, above the five-year average, IEA said, adding total oil supplies from the United States are expected to increase by 1.6 million bpd this year.