General Motors on Tuesday said U.S. sales fell 24 percent in June, attributing the decline to a cutback in fleet sales to daily rental companies, a "soft industry" and lower incentive spending.
The results were considerably lower than analysts' forecast of a 6 percent decline for the month, reported CNBC's Phil LeBeau.
The news came as an industry group reported that automakers across the board are deepening discounts to entice consumers to buy cars.
GM said it sold 326,300 vehicles in the U.S. last month. The results were adjusted for an extra selling day this year.
Meanwhile, Toyota Motor said its U.S. sales rose 6.1 percent on an adjusted basis in June, as incentives helped boost sales of its Tundra pickup truck.
The Japanese automaker, which has overtaken General Motors as the world's largest, sold 245,739 vehicles in the United States in June.
The automaker said car sales rose 5 percent, driven by big increases in sales of its Camry sedan and the Prius hybrid vehicle. Truck sales rose 7.8 percent, boosted by a big increase in sales of the new Tundra pickup.
The results include both Toyota and Lexus brands.
Ford Motorreported a U.S. sales decline of 11.5% in June, adjusted for the number of selling days in the month, as a big decline in car sales more than offset a slight rise in truck sales.
Ford, the second-largest U.S. automaker, said it sold 247,599 vehicles in June, compared with 269,404 vehicles in the same month last year.
Results for Ford -- which had sought to curb its lower-margin fleet sales to car rental companies -- include its import brands and some medium- and heavy-duty trucks.
Sales at the Chrysler Group unit of DaimlerChrysler fell 5 percent on an adjusted basis to 183,347 vehicles. Chrysler Group consists of Jeep, Dodge and Chrysler brands.
The German automaker, which is in the process of selling Chrysler Group, said it sold 202,936 vehicles in June.
Automakers Deepen Discounts
Separately, industry tracking service Edmunds.com said Tuesday that automakers deepened the discounts and rebates on offer to U.S. consumers in June from a month earlier, adding incentives to slow-selling minivans and trucks.
Edmunds estimated the three Detroit-based automakers spent a combined $2.6 billion on sales incentives in the past month, while Japanese automakers spent $823 million.
All of the six leading automakers offered bigger discounts in June than they had in May with the exception of General Motors, Edmunds said.
In a significant departure from usual practice, the three leading Japanese automakers all stepped up their discounting in the face of slack demand, Edmunds said.
"The competitiveness of the marketplace seems to be catching up with the Japanese heavyweights,'' Edmunds analyst Jesse Toprak said in a statement.
Toyota announced in mid-June that it had begun offering rebates of up to $3,500 or interest-free loans for five years on its all-new Tundra pickup truck.
Edmunds estimated that Toyota's average incentive was $1,308 per vehicle in June, up from $1,128 in May.
Chrysler, which has been offering deals for months to support sales of its aging minivan and truck line-ups, had the industry's highest incentives at $3,962 per vehicle in June, up from $3,831 in May, Edmunds said.
Auto sales incentives are widely tracked by analysts as an indication of the relative profitability of competing automakers and the pressure that they face to move inventory.
Automakers do not typically disclose how much they spend on incentives, which can include concessional financing, cash rebates or additional payments to dealers.
Both Ford and GM rolled out end-June summer sales campaigns featuring interest-free financing on a range of vehicles aimed at boosting sales results.
Edmunds estimated that Ford's average incentive spending rose to $3,187 in June from $2,942 in May.
Both GM and Ford headed into the year with a strategy of throttling back on incentive spending as part of a strategy to move away from the kind of blowout sales and volatile results that dogged their results earlier this decade.
Rounding out the six major automakers, Edmunds estimated that Honda Motorhad spent an average of $1,397 on incentives in June, from $1,300 in May.
It estimated average incentive spending for Nissan Motor at $2,218, from $1,943 in May.
By segment, the biggest deals were on minivans, which carried an average discount of $3,900, and full-size trucks, which had an average incentive of $3,864, Edmunds said.