DETROIT— General Motors Co. sold 1,529 battery-powered Chevrolet Volt cars last month, a 34 percent increase from November, amid a U.S. investigation into whether the car's battery poses a fire risk.

More than one-third of those sales were to corporate fleets; a larger proportion than in previous months when about 10 percent of Volts were bought by corporate and other fleet customers. GM said last month was the first time the company had enough supply to fill orders from corporate buyers, which pay the same price as retail buyers, according to The Wall Street Journal.

The auto maker, worried that the investigation could hurt sales of its high-stakes car, is watching Volt sales closely as it pushes for a resolution to questions a from federal safety regulators about whether the battery could catch fire following a severe crash.

"There has been uncertainty in the market, but we believe that uncertainty will go away," said Alan Batey, vice president of sales and service for Chevrolet. He said sales will rise as more of the vehicles becomes available.

GM missed its target of 10,000 sales for 2011, the Volt's inaugural year, by about 2,300 sales. The auto maker says a supply shortages hampered sales and the company has adjusted the way it allocates cars to dealers in an effort to make sure cars are going to the places where demand is highest.

The National Highway Traffic Safety Administration started an investigation into the Volt's lithium-ion battery pack in November after three of the batteries sparked or caught fire days or weeks after being severely damaged in crash tests. GM has said a coolant leak is behind the problem and it is working on a fix.

The auto maker is targeting 45,000 U.S. Volt sales in 2012. It also plans to export 15,000 of the Detroit-built cars to Europe.

Nissan Motor Co. sold 954 Leaf electric cars in December, bringing its annual tally to 9,674.

GM on Wednesday said its December U.S. auto sales rose 4.6 percent, to 234,351, from a year ago. Full-year sales increased 13 percent to 2.5 million.