TOKYO (AP)--Toyota is struggling to keep up with booming demand for hybrid vehicles because it's unable to make enough batteries that are key parts in the hit "green" cars, a senior executive said Monday.

The crunch on battery production is likely to stay for the rest of the year, as new lines can't be added to boost production until next year, said Toyota Motor Corp. Executive Vice President Takeshi Uchiyamada, who oversees production at Japan's top automaker.

"Hybrids are selling so well we are doing all we can to increase production," he told The Associated Press. "We need new lines."

Battery production is critical in determining how many hybrid vehicles Toyota can produce, Uchiyamada said at the company's Tokyo office.

Hybrids, including Toyota's hybrid top-seller Prius, offer better mileage than comparable regular cars by switching between a gas engine and an electric motor.

Toyota leads the world's automakers in hybrids sold at about 1.5 million vehicles since coming out with the first mass-produced hybrid Prius about a decade ago.

Prius and other hybrids are soaring in popularity around the world amid surging gasoline prices, and other automakers are also rushing to produce hybrids. Hybrids also boast a green image in reducing emissions linked to global warming.

But Uchiyamada, who is spearheading a widespread effort at Toyota to make auto production greener, acknowledged such efforts hadn't yet extended to battery production because of the sheer problems in keeping up with demand.

"That has to settle down first," said Uchiyamada, an engineer who played a key role in the development of the Prius.

Toyota said last week its hybrid-battery joint venture with Matsushita Electric Industrial Co., which makes Panasonic products, will begin producing next-generation lithium-ion batteries in 2009, and move into full-scale production in 2010.

Toyota also said it's setting up a battery research department later this month to develop an innovative battery that can outperform even that lithium-ion battery.
Toyota has also announced its third plant in Japan for producing current hybrid batteries, called nickel-metal hydride, packed in the Prius and other hybrid models on sale now.

Lithium-ion batteries, now common in laptops, produce more power and are smaller than nickel-metal hydride batteries. Toyota has said lithium-ion batteries will be used in Toyota plug-in hybrids, which can be recharged from a home electrical outlet.