LONDON (Reuters) — Tension between Iran and the West is likely to keep oil prices high despite a significant improvement in world supply and a big buildup of oil stocks, the International Energy Agency said on Friday.

The agency, which advises 28 industrialized nations on energy policy, said the soaring global oil supply from OPEC countries and the United States far outpaced global demand, curbed by poor economic activity in developed nations.

The agency said global oil supply rose to 91 million barrels a day in April, an increase of 600,000 barrels a day from March. But it said in its monthly oil market report that uncertainty remained because of “geopolitical risks.”

In March, North Sea Brent crude futures rose above $128 per barrel as investors worried that a conflict between Iran and the West could cut off oil supplies from the Middle East.