Ryanair plunged into loss in the first three months of the financial year after what it called the most challenging period in its history.
With more than 99% of its fleet grounded because of the pandemic, the airline reported a loss of €185m (£169m) over the April-to-June period.
That compared with a profit of €243m a year earlier.
Ryanair said it expected to clear more than 90% of refunds for cancelled flights by the end of July.
Airlines have been struggling because of global travel restrictions aimed at halting the spread of the coronavirus.
Ryanair announced in May it was set to cut 3,000 jobs across Europe.
However, earlier this month, the company revealed that it had cut a deal with the Unite union, including temporary pay cuts, so that UK cabin crew jobs would be safeguarded.
The airline later said it was shutting its base at Frankfurt Hahn airport after German pilots voted to reject pay cuts.
In its latest results statement, Ryanair repeated its criticism of rival airlines for receiving what it called “illegal state aid” to stay in business.
“Many other airlines are cutting capacity, with the result that air travel in Europe is likely to be depressed for at least the next two or three years,” it added.
“This will create opportunities for Ryanair… to grow its network and expand its fleet, to take advantage of lower airport and aircraft cost opportunities that will inevitably arise.”