Traffic, measured in revenue passenger kilometres, rose 9.2 per cent versus June 2010, while passenger load factor – a measure of how well it fills its planes – was up 1.8 percentage points at 81.7 per cent.
IAG said part of the rise in June traffic was due to favourable comparisons from a year earlier, when strike disruption hit BA’s passenger numbers and network restructuring impacted Iberia’s figures.
IAG added that the underlying revenue trend was in line with last month.
Europe’s second-biggest airline group by value said its first and business-class travel – the most profitable part of its passenger business -- rose 25.2 per cent, while non-premium traffic was up 6.7 per cent.
IAG’s premium growth follows last month’s warning by industry body IATA that first and business class travel would likely slump because of Japan’s nuclear crisis, weakening world trade and Middle East turmoil.
IAG shares closed up 0.3 per cent at 258.7p, broadly in line with the FTSE.
Meanwhile, budget rival Ryanair unveiled a nine per cent year-on-year rise in traffic during June, bringing its monthly passenger total to 7.3m. Its passenger load factor remained steady at 84 per cent.