WASHINGTON - In the latest in an escalating string of safety problems, Toyota plans to recall 270,000 of its  popular Prius hybrid in the United States and Japan over a braking issue, the Nikkei News Service reported.

A spokesman at Toyota’s U.S. sales division said he had no information to confirm the report from Japan.

“We have no information on any decision to recall the Prius,” said John Hanson, a Toyota spokesman at the company’s U.S. sales arm in Torrance, Calif. He said the company is working with the National Highway Traffic Safety Administration on a preliminary evaluation of the problem.

The news of the possible recall comes after the Transportation Department opened an investigation into dozens of complaints over braking problems affecting the new, third-generation 2010 Prius, especially when the car goes over potholes or rough roads.

Toyota earlier Thursday acknowledged design problems with the brakes in its prized gas-electric hybrid, but said it was still deciding how to inform customers and whether a recall is needed. Toyota said it has already corrected problems with the antilock brake system in Prius models sold since late last month, including those shipped overseas.

NHTSA said it has received 124 reports from consumers about the Prius brakes, including four reports of crashes. The investigation will look into allegations of momentary loss of braking capability while traveling over uneven road surfaces, potholes or bumps.

The new version of the Prius went on sale in May 2009.

The Prius issue represents another setback for Toyota, which has been battered by two major recalls covering some 8 million vehicles in the United States and abroad. Those involve gas pedals that can get trapped under floor mats or become stuck on their own and fail to return to the idle position. The safety probes have challenged Toyota’s longstanding reputation for building safe, quality vehicles.

The Prius was not part of the recall over potentially sticking gas pedals in eight top-selling models including the Camry.

NHTSA said investigators have talked to consumers and conducted pre-investigatory field work on the Prius. The preliminary evaluation involves about 37,000 vehicles in the United States.

“Safety is our top priority,” said Transportation Secretary Ray LaHood. NHTSA said LaHood spoke with Toyota President Akio Toyoda late Wednesday and was assured by the executive that Toyota was taking the safety concerns seriously.

Toyota said in a statement it would fully cooperate with NHTSA’s investigation.

spokesman in Japan, said the time lag for brakes kicking in felt by drivers stem from the two systems in a gas-electric hybrid — the gas-engine and the electric motor.

When the car moves on a bumpy or slippery surface, a driver can feel a pause in the braking when the vehicle switches between the traditional hydraulic brakes and the electronically operated braking system, he said. The brakes work if the driver keeps pushing the pedal, he said.

Toyota acknowledged the brake problem while reporting a $1.7 billion profit for its October-December quarter.

Shares of Toyota traded in the U.S. have declined about 22 percent since Jan. 21, when Toyota announced an expanded recall over the gas pedal issues.

Toyota senior managing director Takahiko Ijichi defended the automaker’s quality standards.

“We have not sacrificed the quality for the sake of saving costs,” he said. “Quality is our lifeline. We want our customers to feel safe and regain their trust as soon as possible.”

Toyota for the first time gave an estimate of the costs of the global gas-pedal recall. The $2 billion total represents $1.1 billion for repairs and $770 million to $880 million in lost sales.

Toyota is expecting to lose 100,000 in vehicle sales because of the recall fallout — 80,000 of them in North America.