General Motors is boosting incentives on the Chevrolet Volt plug-in hybrid to spur sales and lower stockpiles amid price cuts and lease deals on the Nissan Leaf and Fiat 500e electric vehicles.

GM is offering cash rebates of $4,000 on the 2013 Volt and $5,000 on the 2012 model. The rebates, offered from June 3 through July 1, are in addition to a $7,500 federal tax credit and $1,500 state tax credit for California residents.

The Volt also is available for lease with $2,399 down and $269 per month for 36 months.

U.S. sales of the Volt fell 4 percent to 1,607 units in May. Through May, Volt volume rose 1 percent to 7,157 units compared with the same period last year.

The average transaction price for the Volt was $40,236 in May, according to Edmunds.com.

In February, Nissan Motor Co. cut the Leaf EV’s base price by $6,400, making the 2013 model’s base price $29,650, including shipping. The average transaction price for the vehicle was $31,947 in May.

“Clearly some of our competitors have been pretty dramatic in their price reductions,” Don Johnson, Chevrolet’s vice president of U.S. sales, said during a media conference call last week. “That may be causing some unnatural sales to their products.”

U.S. Leaf sales have nearly tripled to 7,614 units this year through May.

Incentives on the Fiat electric 500e include the same monthly lease payment as the base 500 vehicles with gasoline engines.

The $32,500 500e can be leased for $199 per month and $999 down for three years.

Dealers had a 162-day supply of the Volt on June 1, well above ideal levels. Chevrolet spokeswoman Michelle Malcho said one of the reasons for the new incentives is to sell off the supply of 2013 Volts to prepare for the 2014 model.

In May, Volt discounts averaged $5,780 per unit while Leaf spiffs averaged $6,625, according to Edmunds.com.

Mike Colias contributed to this report