Airline passenger traffic jumped nearly 6% in September over the same month last year but industry leaders worry that future numbers won't be as positive.

The International Air Transport Assn., the trade group for the world's largest airlines, reported the September increase but said economic uncertainty in Europe and proposed tax increases in the U.S. could jeopardize future growth and profits.

While passenger traffic increased 5.6% in September, air freight traffic dropped 2.7% in the same month, marking the fifth straight decline, according to the trade group.

The trade group attributed most of the increase in global passenger traffic to growth in emerging markets, such as Latin America, where demand jumped 10.6%, according to the trade group. A weak euro may have prompted more travel into Europe, sparking a 9.2% increase in traffic among European-based airlines, according to the group.

In North America, demand increased only 1.2% in September, compared with the same month last year, the association said.

IATA's director general, Tony Tyler, said economic uncertainty and a proposal by the Obama administration to increase taxes on airlines could cut into growth and future airline profits.

"September's strength in passenger demand was a pleasant surprise," Tyler said. "We are still expecting a general weakening in passenger traffic as we head toward the year-end."