Honda Motor Co. will join Toyota Motor Corp. and Nissan Motor Co. in the race to launch electric vehicles in the United States in the first half of next decade, sources said Saturday.

Honda is planning to begin full-fledged development of electric vehicles because the U.S., which is Japan's biggest car market, is expected to tighten environmental regulations in the future, the sources said. Honda will also consider marketing electric vehicles in Japan, they said.

Toyota and Nissan have already announced plans to launch electric cars. Toyota plans to sell them in the U.S. starting in 2012, while Nissan is seeking to begin mass-production in 2010 for release in the Japanese, European and U.S. markets.

At its group's technological development base in Tochigi Prefecture, Honda has been designing electric vehicles ranging in size from subcompacts to small cars. It is also working to present a prototype at the Tokyo Motor Show this fall, the sources said.

The development comes as calls rise for more environment-friendly vehicles. Among them, the state of California is urging automakers with high sales volumes to enhance marketing of zero-emission cars.

So far, Toyota and Honda have been leading the field for gas-electric hybrids with their popular Prius and Insight models, but Honda has apparently determined that it needs to diversify its "green" car lineup with electric vehicles, the sources said.

Honda, however, will keep its global hybrid expansion plan alive. Even if its begins full-fledged development of electric vehicles, hybrids are likely to remain a core product, a senior Honda official said.