President Barack Obama has observed a moment of silence at a Sept. 11 memorial in New York where the World Trade Center once stood.

Obama and first lady Michelle Obama joined former President George W. Bush and his wife, Laura, at a reflecting pool where the north tower used to be.

They walked along the edge of the pool and stood silently before greeting relatives of the victims of the attacks.

New York had the highest death toll of the three locations attacked on Sept. 11, 2001.