US authorities on Thursday ordered a probe into braking problems in Toyota's Prius hybrid, piling fresh woe on the world's top carmaker already facing a two-billion-dollar bill from massive safety recalls.
The brake trouble comes after accelerator pedal problems that have now spread to Britain and raised fresh questions if Toyota compromised on quality in its drive to overtake General Motors as global number one.
The US National Highway Traffic Safety Administration said it was investigating the electric-petrol hybrid Prius for "momentary loss of braking capability while traveling over an uneven road surface, pothole or bump."
It said there had been 124 reports from consumers, "including four reports alleging that crashes occurred" on Prius, the world's most popular hybrid car.
"Investigators have spoken with consumers and conducted pre-investigatory field work," the agency said in a statement.
The Prius -- which combines a petrol combustion engine with a battery-powered electric motor -- is Toyota's flagship hybrid car and key to its efforts to stay in pole position in fuel-efficient vehicles.
US Transportation Secretary Ray LaHood also evoked the safety of Toyota cars and trucks in a talk with comany chief Akio Toyoda, US officials said Thursday.
"Late Wednesday, Secretary LaHood spoke with Toyota president, Akio Toyoda, who reassured him that Toyota takes US safety concerns seriously and puts safety at the top of the company's priorities," the transportation department said in a statement.
Toyota said it had redesigned the anti-lock braking system (ABS) -- designed to prevent skidding -- for the latest version of its Prius produced since last month and would soon announce steps for those already on the road.
At a hastily scheduled news conference, Toyota said it would soon unveil safety measures relating to the Prius brakes.
"We'll make an announcement before long," said Hiroyuki Yokoyama, a Toyota official in charge of quality control. "The brakes are slow but if you continue to step on them, the car will stop."
Toyota denied it had dragged its feet on revealing the fault, saying the initial reports of trouble were only received late last year when icy conditions in Japan and North America contributed to the problem.
The flaw could hardly have come at a worse time for the Japanese giant.
Toyota is under fire in the United States for its handling of massive recalls affecting about eight million vehicles worldwide -- more than its entire 2009 global sales of 7.8 million vehicles -- due to accelerator trouble.
Despite the huge recalls, the Japanese giant said it was on course to earn 80 billion yen (880 million dollars) this fiscal year after posting a net profit of 153.2 billion yen in October-December.
But recall costs and lost sales are expected to slash profits by up to about 180 billion yen (2.0 billion dollars) in the current financial year to March, the company said as it came in for ferocious criticism in the United States.
The gas pedal problems have been blamed for several accidents, including an August crash in California in which four family members were killed when their Lexus sped up on a highway and crashed in a ball of flames.
Toyota said it was also now recalling cars in Britain across seven model ranges owing to the faulty accelerators. A company spokeswoman said Toyota was seeking contact details for all 180,865 Toyota owners in Britain.