ATLANTA - Delta Air Lines Inc said on Thursday that it planned additional cuts in seat capacity this year as rising fuel prices and softer travel demand pressure business.

The world's biggest airline also said the planned capacity reductions meant it must again reassess staffing needs, but added it would try to avoid involuntary layoffs.

In a statement, Atlanta-based Delta said it planned to reduce system capacity by 10 percent from 2008, with reductions beginning in September.

It also said it planned to cut international capacity an additional 5 percent on top of what it has already announced, for a total reduction of 15 percent. Earlier this year, Delta had said it would cut international capacity by 10 percent.

The company also said it would accelerate the merger integration with Northwest Airlines and keep tight controls on costs and spending.

The carrier cited cost pressures from rising jet-fuel prices and said the H1N1 flu virus outbreak contributed to softer travel demand.

Delta shares were down 1.8 percent at $6.43 in morning trading as other airline stocks fell. United parent UAL Corp (UAUA.O) was off more than 4 percent, while US Airways Group Inc (LCC.N) and American parent AMR Corp (AMR.N) each fell more than 2 percent. (Reporting by Karen Jacobs; Editing by Lisa Von Ahn)