"Yes, we were all Americans on that day," Hollande wrote on his Facebook page.
According to the French President, the US reciprocal measures have just increased the terrorist threat.
"The reciprocal measures taken by the US administration in response to these planned attacks, which were methodically performed on its territory have not eradicated the threat, vice versa its has expanded the scale of the threat, especially in Iraq," Hollande said.
Hollande reminded that France did not support the intervention and even condemned it, though Paris suffered the consequences of the "chaos engendered by this".
Sunday marks the 15th anniversary of the 9/11 terrorist attacks on New York's World Trade Centre and the Pentagon in Washington. As a result of the attacks, nearly 3,000 people were killed and another 6,000 were injured.