More than 342,000 cars made by Mazda Motor Corp and Bayerische Motoren Werke AG  are under investigation by the U.S. auto safety regulator for possible steering defects that could lead to loss of vehicle control.

The National Highway Traffic Safety Administration said on Friday it opened probes into 293,787 Mazda3 cars from the 2007 to 2009 model years, and 48,764 BMW Z4 sports cars from 2003 to 2005.

In both cases, NHTSA is in the earliest stages of a formal review that could lead to recalls. The agency has stepped up its probes into possible vehicle defects after a massive safety crisis at Toyota Motor Corp led to the recall of more than 10 million vehicles worldwide.

Toyota earlier said on Friday it would recall 270,000 Lexus and Toyota cars to replace faulty valve springs that may cause engine stalling.

NHTSA said it received 33 complaints about Mazda3 models that alleged a loss of power steering assist while driving, requiring excessive force by the driver to main control. Three of the complaints alleged that the loss of steering control caused crashes. The vehicle uses an electrically actuated hydraulic power steering system, the agency said.

On the BMW Z4s, NHTSA said it received 107 complaints alleging a loss of power-assisted steering. The complaints stated that the steering wheel sticks, binds or locks up, requiring increased steering effort to maintain control and increasing the potential to over-steer the vehicle.

The failures typically occurred at higher vehicle speeds over 45 miles per hour and at warmer temperatures above 75 degrees F. One complaint involved a crash, and several complaints reported loss of vehicle control or near-miss incidents.

There were no fatalities reported among the Mazda3 and BMW Z4 complaints, the agency said.

(Reporting by David Lawder, editing by Philip Barbara)