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 said.

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' downtown Detroit headquarters, Whitacre would not answer questions, but said the board and Henderson agreed that he should step down.