DETROIT – GM's board and CEO Fritz Henderson parted ways Tuesday, the board upset that the automaker's turnaround wasn't moving more swiftly and Henderson frustrated with second-guessing, two people close to the former CEO told The Associated Press.

Board Chairman Ed Whitacre Jr., the former head of AT&T Inc., will take over as CEO while a global search is conducted.

It was unclear whether Henderson or the board moved first in the surprise resignation, which came just hours before Henderson was to be the high-profile keynote speaker at the Los Angeles Auto Show. At a hastily called news conference at General Motors Co.'s downtown Detroit headquarters, Whitacre would not answer questions, but said the board and Henderson agreed that he should step down.

Whitacre thanked Henderson, 51, a lifelong GM employee, for his leadership and said the company is on the right path toward offering high-quality cars and trucks worldwide.

Both men were chosen for their jobs by the U.S. government, which owns more than 60 percent of the Detroit automaker in exchange for giving it billions in loans. But Henderson is a GM insider, while Whitacre had no car experience before taking the GM chairmanship.

"I don't think this has much to do with Fritz Henderson's performance, I think it's just the wrong time to be a GM lifer," said Logan Robinson, a former Chrysler attorney and professor of corporate governance at University of Detroit Mercy.

Industry analysts said GM likely would look for someone like Ford Motor Co. CEO Alan Mulally, who was hired in 2006 from aerospace giant Boeing Co. Mulally also had no automotive experience, but unlike Whitacre, was well-versed in manufacturing.