As part of a fresh investigation into the beleaguered carmaker's conduct, US authorities have sought documents from Toyota on Tuesday over its handling of a series of safety recalls.

The US National Highway Traffic Safety Administration (NHTSA) is looking into whether Toyota Motor Corp acted quickly enough in responding to safety concerns over sticky accelerator pedals and faulty brakes in a number of models.

US Transportation Secretary Ray LaHood said in a statement," Safety recalls are very serious matters and automakers are required to quickly report defects."

The Japanese manufacturer's sales tumbled in January amid the recall controversy and Toyota said it would briefly halt production at two plants, one in Texas and one in Kentucky, because of a backlog of vehicles at dealerships.

Toyota which have led the world's largest carmaker to recall more than 8 million vehicles worldwide over the past few months, is required to hand over documents to the NHTSA showing when and how it learned of the defects, which have led the world's largest carmaker to recall more than 8 million vehicles worldwide over the past few months.

The Transportation Department on Monday said the number of deaths linked to unexpected acceleration by Toyota cars had risen to 34 in the United States. The updated figure followed a wave of publicity about the problem.