In a letter to President Barack Obama, Bryson said he would leave the cabinet because the June 9 seizure "could be a distraction from my performance as Secretary."

"Our country would be better served by a change in leadership at the Department," he continued.

Bryson is under a felony investigation in California over the two hit-and-run incidents.

At the time the Los Angeles County Sheriff's Department said Bryson's Lexus rear-ended another car as it waited at a railway crossing in the city of San Gabriel.

Bryson then spoke to three males in the damaged car and drove away, hitting their Buick again in the process.

He then drove to the city of Rosemead, where he struck a second car, said officials, who said the secretary later was found "alone and unconscious behind the wheel of his vehicle." No one was injured in the crashes.

But the 68-year-old took a medical leave of absence afterward.

He told staff early Thursday that he would be replaced, at least temporarily, by current deputy secretary Rebecca Blank, who has served in his place since the accidents.

Bryson was tapped for the cabinet post last year as part of Obama's effort to mend ties with business and to get the US economy back on track.

He had a long resume in industry, including stints on the boards of Boeing and Walt Disney.

In a statement Thursday Obama praised Bryson's work.

"I want to extend my deepest thanks and appreciation to John for his service over the past months, and wish him and his family the very best," the president said in a statement.

"As secretary, John fought tirelessly for our nation's businesses and

workers, helping to bolster our exports and promote American manufacturing and products at home and abroad."