By Emma Ross-Thomas and Paul de Bendern

ISTANBUL (Reuters) - The global airline industry is set to turn to a loss this year, possibly as high as $6.1 billion (3.1 billion pounds), as carriers struggle with sky-high fuel prices, the International Air Transport Association (IATA) said on Monday.

"The situation is desperate and potentially more destructive than our recent battles with all the horsemen of the apocalypse combined," IATA Director General Giovanni Bisignani said in a speech at an annual meeting held this year in Istanbul.

As recently as April the IATA forecast an industry profit of $4.5 billion. In 2007 profits reached $5.6 billion.

"If we see $135 oil for the rest of the year, losses could be $6.1 billion," said Bisignani.

IATA said in its annual report that a combination of high fuel prices, a U.S. economic downturn and accelerated deliveries of aircraft ordered at the peak of the economic cycle but delivered during the slowdown meant the outlook for 2008 was "clouded by the perfect storm."

Oil prices, which hit an all-time high of $135.09 a barrel on May 22, threaten the industry's outlook. Oil prices have roughly doubled in the past year.

Already suffering, U.S. airlines have raised fares, added fees and surcharges, cut jobs and reduced services to cope with oil prices and the slowdown.

European industry officials said ticket prices would have to rise and capacity would be cut, while low-cost carriers would be hardest hit as a larger slice of their costs comes from fuel.