WASHINGTON (Reuters) - CIA Director David Petraeus resigned as head of the main U.S. spy agency on Friday, saying he had engaged in an extramarital affair and acknowledging that he "showed extremely poor judgment."
In a letter to the CIA workforce, Petraeus, 60, said that he met with President Barack Obama at the White House on Thursday and asked "to be allowed, for personal reasons, to resign from my position."
"After being married for 37 years, I showed extremely poor judgment by engaging in an extramarital affair," he wrote. "Such behaviour is unacceptable, both as a husband and as the leader of an organization such as ours."
Obama, who was re-elected to a second term on Tuesday, said in a statement that he accepted Petraeus' resignation, praising him for his work at the CIA and for leading U.S. troops in Iraq and Afghanistan.
The sudden and dramatic turn of events appeared to end the public career of a widely admired man who played a key role in the Iraq war, led the U.S. Central Command and commanded U.S. and NATO troops in Afghanistan.
Petraeus' name had circulated speculatively as a possible Republican presidential nominee before Obama tapped him as CIA chief. Before taking the CIA post, he retired as an Army general after nearly four decades of military service.
Petraeus had led the CIA for only 14 months. His sudden departure threatened to usher in a period of instability at the spy agency, which is grappling with a levelling off in its budget after a decade of steady increases.
The agency is also fending off questions about its performance before and after the attack that led to the death of U.S. Ambassador Chris Stevens in Benghazi, Libya.
U.S. officials insisted that the CIA's handling of the Benghazi incident had nothing to do with Petraeus' decision to resign.
TESTIFY ON CAPITOL HILL
Petraeus had recently travelled to Libya and the Middle East, and had been scheduled to testify about the Benghazi events next week behind closed doors to the House and Senate intelligence committees.
In his statement, Obama said, "I am completely confident that the CIA will continue to thrive and carry out its essential mission."
But there is no indication that he broke any agency rule in connection with his admitted affair, sources familiar with the matter said. The CIA has no broad rule banning officials from engaging in extramarital affairs, though if discovered, liaisons by CIA personnel with suspected foreign agents would pose security problems for a U.S. spy.
Obama, who accepted Petraeus' resignation in a phone call with him Friday afternoon, said that Michael Morell, the agency's long-time deputy director, would serve as acting CIA chief.
Morell, who is well respected at both the White House and on Capitol Hill, had previously served as acting director following the departure of former CIA chief Leon Panetta.
He is a leading candidate to be Petraeus' permanent successor, sources said. Other possible candidates being discussed on Capitol Hill include John Brennan, Obama's chief counter-terrorism adviser; Obama national security adviser Thomas Donilon; and former congresswoman Jane Harman, who chaired the House intelligence committee.
Petraeus' resignation also adds a new vacancy on Obama's national security team. Secretary of State Hillary Clinton has said she will leave after Obama's first term, and Defence Secretary Leon Panetta is widely expected to leave as well.
Petraeus' wife, Holly, has been an advocate for U.S. veterans and head of the Office of Servicemember Affairs at the U.S. Consumer Financial Protection Bureau.
Last month, Petraeus and Holly appeared together at a reception at the Canadian Embassy in Washington to celebrate the premiere of the Ben Affleck film "Argo," which chronicles a successful operation in which the CIA and Canadian diplomats smuggled a group of U.S. officials out of Tehran during the 1979-80 U.S. Embassy hostage crisis.