The company said that, as a result, it is "redoubling" its efforts to replace the defective Sony battery packs in certain of its notebook models.

"On May 24, 2007, a Toshiba portable computer with a Sony battery pack caught fire," Toshiba said in a statement. After asking Sony to investigate, Toshiba said, the "investigation confirmed that the cause of the fire was the battery pack, as in other incidents reported earlier. . . While the primary cause of the fire in the May 24 incident was not identified, damage resulting from a short circuit within the battery pack was found, confirming that the problem originated in the battery pack."

The company also revealed the April incident "involving an unreplaced battery pack," but provided no further details.

Millions of Sony battery packs were recalled by manufacturers including Dell, Apple, Toshiba, Lenovo and Fujitsu last year, after a series of high-profile meltdowns and fires. In one incident that sparked worldwide attention, a Dell notebook burst into flames at a public conference in Japan and a photograph of that incident circulated on the Internet for months. After an investigation by Dell, Sony and the U.S. Consumer Product Safety Commission, Dell called for a recall of 4.1 million notebook batteries and was subsequently followed by the other vendors.

Toshiba said the battery packs in affected notebooks, that still have not been replaced, will be replaced for free.

The PC maker maintains a list of affected notebooks and battery packs on its web site.