Japan's attempts to weaken the yen in foreign-exchange markets give its automakers "an unfair advantage" in the United States, a top executive of General Motors Corp. said Tuesday.

GM Vice Chairman John Devine, who is in Japan to attend the Tokyo Motor Show, which opens to the public Saturday in Chiba Prefecture, said this intervention has given Japanese manufacturers "a windfall profit."

"The practice of intervening in the currency market to benefit exporters is not fair," Devine, chief financial officer at the U.S. auto giant, told a news conference in Tokyo.

Japan has spent more than a $100 billion this year on keep its currency low against the dollar, which "creates a windfall profit for Japanese auto companies," Devine said.

The value of the yen against the dollar should stand at "100 or probably stronger," he said. Devine added that GM plans to strengthen its cooperation with three Japanese affiliates in an effort to boost car sales in Japan.