US President Barack Obama will mark the 10th anniversary of 9/11, by visiting each of the three sites of the terrorist attacks, White House press secretary Jay Carney announced. "Throughout the day he will pay tribute to those we lost," Carney said. Obama will travel to Ground Zero in New York City, where the World Trade towers had stood, the site of the Flight 93 memorial in Shanksville, Pa., and the Pentagon. He will be accompanied by First Lady Michelle Obama. The 10th anniversary of the 9/11 attacks comes four months after the killing of al Qaeda leader Osama bin Laden. In New York, the president will be joined at Ground Zero by former President George W. Bush, former New York City Mayor Rudy Giuliani, as well as the current Mayor Michael Bloomberg. Since taking office, Obama has spent previous anniversaries at the Pentagon. He laid a wreath at Ground Zero in May after bin Laden’s death. He has not been to Shanksville as president. Carney said Vice President Joe Biden will attend the groundbreaking of the Flight 93 memorial on Sept. 10.