The head of the Secret Service -- the police agency that protects President Barack Obama -- is retiring, a spokesman said Friday, just months after the elite squad was hit by a sex scandal.

Mark Sullivan is "retiring as of the 22nd of February," Secret Service spokesman Brian Leary told AFP, noting he had overseen 23 national security events, including the 2009 inauguration of President Barack Obama.

Sullivan, who took up his post in May 2006, saw the end of his term marked by a series of setbacks, most recently a prostitution scandal that erupted in April as agents helped prepare Obama's visit to a summit in the Colombian port city of Cartagena last year. Nine officers resigned or retired in the wake of the scandal.

Hundreds of Secret Service agents typically travel with, or before Obama when he goes overseas, in a huge security retinue.

April's incident was embarrassing to the Obama administration and led to allegations that national security or the president's safety might have been compromised.

Sullivan had to testify in Congress to assure that no security breaches were committed during the scandal. In its wake, the Secret Service announced it had toughened the rules regulating behavior of its agents abroad, including the consumption of alcohol and meetings with strangers.

Sullivan earlier found himself in the hot seat in 2009 after socialite and reality star Michaele Salahi and her husband Tareq breezed through White House security at a state dinner for Indian Prime Minister Manmohan Singh.