The head of the security agency guarding US President Barack Obama has resigned under fire after a series of security lapses came to light involving the president's protection.

Homeland Security Secretary Jeh Johnson announced on Wednesday the resignation of Secret Service Director Julia Pierson, and said Joseph Clancy, a veteran of the agency, was named acting director.

White House spokesman Josh Earnest said Obama had called Pierson to express his appreciation to her for her long years of service.

He said Obama had concluded that new leadership was needed at the agency after a number of security lapses, including a White House fence-jumper who managed to enter the front door of the mansion on September 19, and get into the ceremonial East Room before off-duty agents stopped him.

It was also reported on Tuesday that the US president had ridden a lift with an armed ex-convict, while visiting the Centers for Disease Control and Prevention in the state of Georgia.

Al Jazeera's Shihab Rattansi, reporting from Washington DC, said that the White House only learned about the security breach in Georgia an hour before the story was published in the Washington Post.

The Post also revealed that it took the Secret Service five days before realising a man had fired shots at the White House in 2011, while one of Obama's daughters was inside.

On Tuesday, Pierson appeared before a Congressional hearing in the US capital, and was repeatedly criticised by members of Congress for the reported breaches.

Source: Al Jazeera and agencies