All regions except for Latin America reported double-digit growth.

Available capacity rose 5.2 percent in May, meaning that load factors rose by 3.0 percentage points to 45.2 percent.

IATA, however, believes the best of the cyclical upturn may have passed.

"With indications that the cyclical growth period may have peaked, the onus is on the industry to improve its value proposition by accelerating process modernisation and enhancing customer-centricity," IATA Director General and CEO Alexandre de Juniac said.

For the third quarter, IATA expects air freight demand to grow by 8 percent. Last month the global airlines association upgraded its full-year forecast for an increase in demand to 7.5 percent from 3.5 percent.

Germany's Lufthansa on Wednesday confirmed its air freight division was doing well in 2017 as the sector benefits from a recovery in global economies and trends such as growth in e-commerce.

(Reporting by Bartosz Dabrowski; editing by Jason Neely)