Moving ahead with a partnership announced in May, Toyota is working on a potential new electric car with California's Tesla Motors, a source at the Japanese automaker said.

Toyota Motor Co. chief executive Akio Toyoda was quoted in media reports from Japan saying that Toyota was working on a prototype electric vehicle based on Tesla's technology. An internal Toyota briefing document obtained by CNNMoney.com confirmed those reports.


Toyota is working Tesla Motors, maker of the Tesla Roadster electric sports car pictured here, to build a new electric vehicle.
It is unclear, however, how far such a vehicle is in development. Toyoda reportedly said details of the program would be released later.

Toyota announced in May that it planned to invest $50 million in Tesla Motors following the electric car maker's initial public offering, which took place on June 29.

Toyota, which is already the industry leader in gas-electric hybrid cars, is also looking for other partners to develop future alternative fuel technologies. Collaboration will be an important part of Toyota's alternative fuel strategy, Toyoda said, according to the document.

Toyota executives have, in the past, expressed doubts about the market potential for purely electric cars, citing their high cost, relatively short driving distance, long charging times and questions about battery technology.

Last year, Toyota revealed a concept version of a tiny electric "city car" with a 40 mile range. That car is under development, Toyota said at the time, and is intended primarily for short-term rental use within cities.

That car, the FT-EV II, illustrated an ideal real-world use for an electric vehicles, Toyota executives said at the time. The Tesla project is apparently a separate project.

Toyota plans to introduce a plug-in version of the Toyota Prius hybrid car in 2011, but that vehicle would still use a gasoline engine as its primary power source.