General Motors Co will pay back roughly $8 billion in debt to the United States and Canada before June, its chief executive said on Wednesday, more quickly than the automaker had promised.

CEO Ed Whitacre said in December that GM would pay back government loans extended to finance its restructuring in bankruptcy by June.

I believe we're going to beat that date, Whitacre said on Wednesday in remarks to the Rotary club in San Antonio, Texas, where he lives.

We have restructured and the progress that we've made, I believe, is sustainable, he said. We're not being crushed under a mountain of debt. We have a cost structure that works.

Whitacre, who has shaken up GM's sales and marketing teams and pushed the top U.S. automaker for faster growth in sales, said there were positive signs that GM's U.S. market share was holding steady after years of decline.

We're right at 20 percent, which is good, he said. We'd like that to increase over time. I can't tell you a percent -- as much as possible.

(Reporting by Jim Forsyth, writing by Kevin Krolicki. Editing by Robert MacMillan)