WASHINGTON (Reuters) - CIA Director David Petraeus has submitted a letter of resignation to President Barack Obama, Director of National Intelligence James Clapper said on Friday.

"Dave's decision to step down represents the loss of one of our nation's most respected public servants," Clapper said in a statement without giving a reason for the resignation.

White House spokesman Jay Carney did not provide any details but said: "We'll have something from the president on it today."

Petraeus said in a message to the CIA workforce that he was resigning because of an extramarital affair.

"After being married for over 37 years, I showed extremely poor judgment by engaging in an extramarital affair. Such behavior is unacceptable, both as a husband and as the leader of an organization such as ours," Petraeus said.