UK airports operator BAA said the euro zone crisis had dented traffic numbers from UK airports to Greece, Spain and other European countries suffering worsening economic conditions.
BAA owns London Heathrow - Europe's busiest airport.
It said passenger numbers between Heathrow and Greece dropped 11.3% in May compared with the same month a year ago.
The numbers to and from Italy fell by 9.2%, Portugal by 11.4% and Spain 2.5%.
"The impact of the euro zone crisis is still being felt with sharp falls in passenger numbers to the worst affected countries and reduced cargo traffic," said BAA's CEO Colin Matthews.
BAA is owned by Spanish infrastructure group Ferrovial. It said cargo traffic - a key indicator of economic health - fell 2.4% across its airports last month. Cargo traffic at Heathrow was down 3.8%.
"Both cargo figures are likely to be a reflection of the continued economic problems, particularly in the euro zone," added Mathews.
IAG, formed by the merger of British Airways and Iberia, last week said worsening economic conditions in Spain hit its performance last month, undermining strength in long-haul travel out of London.
Traffic at airports operated by BAA fell 0.1% in May, compared with the same month in 2011, reflecting last year's late Easter and the royal wedding which boosted traffic in May 2011. The late May bank holiday into June this year also reduced last month traffic figures, it said.
BAA said 5.8 million passengers passed through Heathrow last month, 0.6% down on last May.
The company, prevented by the government from building a third runway at Heathrow because of environmental concerns, has seen traffic to emerging markets rise in recent years and believes it is now falling behind rival European airports in the battle for these lucrative routes because of constraints on growth.
BAA, which also owns Southampton in the south of England, and Glasgow and Aberdeen airports in Scotland, said the euro zone crisis showed why Britain urgently needed to build better links to the countries whose economies are growing such as China, India and Brazil.
"With the UK's only hub airport, Heathrow, already full, France and Germany are forging ahead and we are being left behind," Matthews said.
