NEW YORK – Americans cut back on soda at an accelerated pace last year, underscoring the difficulties Coca-Cola and PepsiCo face in winning back customers.

U.S. sales volume of carbonated soft drinks fell 3 percent in 2013, extending a streak of declines that began nearly a decade ago. It also represents a steeper drop than the 1.2 percent decline in 2012 and the 1 percent drop in 2011, according to an annual report by Beverage Digest, an industry tracker.

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Empty and crushed soda cans build up on a conveyer belt near the end of the line at Tennis Sanitation in Saint Paul Park, Minn. Americans cut back on soda again in 2013, extending a trend that began nearly a decade ago. 2014 Associated Press File Photo

Carbonated soft drinks still represent the biggest category in the beverage industry. But the popularity of longtime favorites like Coke, Pepsi and Dr Pepper is waning as a growing number of alternatives like flavored waters and energy drinks pop up in beverage aisles. Soda has also been under fire from public health advocates for fueling weight gain.

Even diet sodas are suffering. Last year, for instance, Diet Coke’s sales volume declined 6.8 percent, compared to a 0.5 percent drop for regular Coke, according to Beverage Digest. Diet Pepsi declined 6.9 percent, compared to a 3.6 percent decline for regular Pepsi.

Industry executives blame the trend in diet sodas on worries people have about artificial sweeteners. But diet sodas are also facing intensifying competition from the proliferation of lower-calorie alternatives, many of which are made with artificial sweeteners as well. Sparkling Ice, a small brand owned by TalkingRain, for instance, last year saw sales more than double, according to IRI, a Chicago-based market research firm.

Overall, Coca-Cola, which also owns Sprite and Fanta, saw its soda volume fall 2.2 percent.

PepsiCo, which makes Mountain Dew, saw volume fall 4.4 percent. That was despite the company’s stepped up marketing for its flagship soda, including sponsorship of the Super Bowl halftime show for the past two years.

Coca-Cola and PepsiCo both make an array of other beverages, including bottled water, orange juice and sports drinks. But sodas still account for a large and lucrative portion of their businesses, and executives have expressed determination in getting sales volume back on the path to growth.

Dan Schafer, a spokesman for Coca-Cola, said the Atlanta company was “committed to returning our overall sparkling business to growth in the U.S.”

A representative for PepsiCo of Purchase, N.Y., didn’t immediately respond to a request for comment.