DUBLIN, July 20 (Reuters) - Ryanair warned on Monday that its average summer fares looked set to be modestly down on last year amid uncertainty around the Iran war, while after-tax profit for the low-cost airline's April-June quarter fell short of analyst forecasts.

Europe's largest airline by passenger numbers reported an after-tax profit of €538 million ($615.6 million) for its fiscal first quarter through June 30, compared with a forecast of €579 million in a company poll of analysts.

At its last quarterly results in May, Ryanair said it was discounting some prices to keep volumes up amid headwinds from the war, and warned fares could be broadly flat between July and September.

First-quarter average fares were 6% lower than the same period last year "as the Middle East conflict led to consumer hesitancy, concerns about EU jet-fuel shortages, economic uncertainty and later bookings," Chief Executive Michael O'Leary said in a statement.

"Despite a recent, slight, uptick in volumes, and less price stimulation, Q2 pricing is trending modestly down year-on-year and the final H1 fare outcome is heavily dependent on the strength of close-in bookings in August and September," he said.

Close-in bookings refer to last-minute reservations, and are generally the main source of profit for budget airlines.

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(Writing by Conor Humphries; Editing by Kevin Buckland)