TOKYO (AP) — Toyota Motor Corp. has been hit by over 100 complaints in the U.S. and Japan about brake problems with the popular Prius hybrid, the latest in a spate of quality troubles for the automaker as it grapples with massive global recalls.

The Japanese company's sales are being battered in the U.S. — Toyota's biggest market — after recalls of top-selling models to fix a gas pedal that can stick in the depressed position.

The new Prius gas-electric hybrid, which went on sale in Japan and the U.S. in May 2009, is not part of the recalls that extend to Europe and China, covering nearly 4.5 million vehicles.

The U.S. National Highway Traffic Safety Administration has received about 100 complaints involving the brakes of the Prius new model. Two involved crashes resulting in injuries.

Japan's transport ministry said Wednesday it has also received 14 complaints since July last year about brake problems with Toyota's new Prius hybrid.

The 14 complaints included an accident in July 2009, in which a Prius crashed head on into another car at an intersection. Transport ministry official Masaya Ota said two people were slightly injured in the accident.

"The Prius driver in the accident told police that a brake did not work," Ota said. "Other Prius drivers also complained brakes were not so sharp." The complaints in Japan involve the new Prius model, and the vehicles were all made in Japan, he said.

The ministry ordered Toyota, the world's No. 1 automaker, to investigate the complaints. The other 13 cases happened from December to January 2010. Ota said the ministry has yet to receive a formal report on the complaints from Toyota.

Toyota spokeswoman Ririko Takeuchi said the company has received reports about the Prius complaints in North America and in Japan and was now looking into the matter.

Toyota shares plunged 5.7 percent to 3,400 yen ($38) with jittery investors dumping stocks in the wake of the Prius woes in the U.S. and Japan. The benchmark Nikkei stock index edged up just 0.3 percent to 10,404.33 as the drop in Toyota dampened sentiment.

"Investors were worried the latest trouble involving the Prius could get bigger. The problem could pose a bigger question on Toyota's quality and safety," said Kazuhiro Takahashi, market analyst at Daiwa Securities SMBC Co. Ltd.

Also Wednesday, the South Korean government said Toyota's local unit was recalling 444 vehicles over defects in gas pedals and floor mats.

The vehicles were made in North America, and the more than 19,000 Toyota vehicles imported from Japan weren't part of the recall, the Ministry of Land, Transport and Maritime Affairs said in a statement.

Toyota is facing growing criticism that it has not done enough to ensure the safety of its vehicles.

U.S. Transportation Secretary Ray LaHood told The Associated Press Tuesday that federal officials had to alert Toyota to the seriousness of the safety issues that eventually led to the recalls.

"They should have taken it seriously from the very beginning when we first started discussing it with them," he said. "Maybe they were a little safety deaf."

LaHood also said the U.S. government was considering civil penalties for Toyota for having dragged its feet on safety concerns.

Toyota executive vice president Shinichi Sasaki acknowledged Tuesday in a Nagoya, Japan, news conference that it took prodding from NHTSA officials for the company to decide on the U.S. recall.

Toyota has long prided itself on sterling vehicle quality and assembly line methods that empowered workers to ensure faultless production.

The latest recall, announced Jan. 21, over sticky gas pedals affects 2.3 million vehicles in the U.S. alone.

Any serious problems emerging in the Prius, Toyota's flagship green car model, is certain to further tarnish its brand.

The Prius, now in its third generation since its 1997 introduction, is the best-selling gas-electric hybrid in the world, racking up a cumulative 1.6 million units sold so far, according to Toyota.

Hybrids, by going back and forth between a gasoline engine and electric motor, tend to offer better mileage in slow-speed and stop-and-go driving that's common in crowded cities.

Toyota executive vice president Shinichi Sasaki acknowledged Tuesday in a Nagoya, Japan, news conference that it took prodding from NHTSA officials for the company to decide on the U.S. recall.

Tokyo, Japan (CNN) -- Without issuing a recall of its iconic Prius hybrid vehicles, Toyota said Thursday a software glitch is to blame for braking problems in the 2010 model.

"We would want to be given a little time," Hiro Yuki Yokoyama, Toyota's managing officer, said when reporters asked whether a recall was in the works.

The company changed its braking system software in January as part of what it called "constant quality improvements," but did not say what it would do about vehicles manufactured before then.

Toyota officials described the problem as a "disconnect" in the vehicle's complex anti-lock brake system (ABS) that causes less than a one-second lag. With the delay, a vehicle going 60 mph will have traveled nearly another 90 feet before the brakes begin to take hold.

Brakes in hybrids such as the Prius operate differently from brakes in most cars. In addition to standard brakes, which use friction from pads pressed against drums or rotors, the electric motors in hybrids help slow them. The process also generates electricity to recharge the batteries.

The Japanese government has warned Toyota to take seriously mounting complaints with the Prius. Toyota Vice President Shinichi Sasaki met with Japan's transport minister on Wednesday.

Toyota officials described the problem as a "disconnect" in the vehicle's complex anti-lock brake system (ABS) that causes less than a one-second lag. With the delay, a vehicle going 60 mph will have traveled nearly another 90 feet before the brakes begin to take hold.