An additional 1.5 million vehicles were being recalled in Japan, along with 496,000 in Europe.
A spokesman for the company in Tokyo said the recalled Prius cars were of the model's second generation. Certain Corolla models are also affected.
Wednesday's recall is the latest embarrassment for Toyota, which last month announced a recall of 7.43 million cars due to a power window problem that posed a fire risk.
That recall was the largest issued by an automaker in years.
In 2009 and 2010, more than 8 million Toyota units were brought in for a potential problem involving sticky accelerator pedals. In that case, dealers were told to suspend sales of eight models, and production of those models stopped temporarily.