A recent escalation of hostilities between the US and Iran could upend the International Energy Agency's (IEA's) forecast of a significant oil market surplus next year, it said on Friday, as global supply jumped in June when the Strait of Hormuz reopened but still lagged pre-war levels.

Global oil markets received some respite last month as a peace agreement between the US and Iran facilitated the opening of the Strait, the effective closure of which had taken out as much as 14-million barrels per day of crude flows during the peak of the largest oil supply crisis in history.

Global oil supply rose by 4.1-million barrels a day in June, the agency said, but remained 9.4-million barrels a day below pre-war levels. The agency predicts supply will expand by 7.5-million barrels a day next year, but this is contingent on improved Hormuz transits.

"An escalation in hostilities on 7 and 8 July, however, clouds the outlook and could upend the forecast that sees the market flipping to a surplus next year," it said.