Former US President George Bush has declined an invitation from Barack Obama to attend an observance at New York's ground zero.
Mr Obama plans to visit the site of the destroyed World Trade Centre on Thursday following the death of Osama bin Laden in a raid by US Navy Seals in Pakistan.
The al Qaida attack on the Twin Towers, which killed about 3,000 people, occurred in the early months of Mr Bush's presidency in 2001.
A spokesman said the former president appreciated the offer to attend but had chosen to remain out of the spotlight during his post-presidency.
But the spokesman added that Mr Bush celebrates bin Laden's death as an "important victory in the war on terror".