"Yes, that day, we were all Americans," Hollande wrote on Facebook of September 11, 2001 – echoing a front-page headline in the Le Monde newspaper at the time.

But the French leader also offered a criticism of U.S. policy in the wake of the attacks.

"The response that the U.S. administration had to these attacks ... far from eradicating the threat, they have expanded it to a wider space. In particular, Iraq," Hollande wrote, referring to the bloodshed that followed the U.S. invasion of Iraq in 2003 and continues to this day. “And even though France, through (former president) Jacques Chirac, rightly refused to join the intervention which it even condemned, it has still been a victim of the consequences of the chaos it caused."

France has suffered a number of terror attacks over recent years, including a series of attacks in Paris last November that left 130 dead. Many of these attacks were claimed or inspired by the Islamic State militant group, which first came to prominence as an insurgency in the aftermath of the Iraq invasion.

Hollande wrote that every terror attack was like a repeat of 9/11, "like a replica of the terror." He advised that "democracy, freedom, tolerance and culture" were the only way to defeat "Islamist fanatics."

Despite French opposition to the Iraq invasion, the country later became deeply involved in a number of other foreign conflicts, including those in Libya and Mali. France has used air strikes to hit the Islamic State in Iraq and Syria since 2014; in the aftermath of the attacks in Paris, this campaign was intensified.

Recent polls have shown that doubts among Americans about the nation's safety after the 9/11 attacks and their aftermath remains strong. In one poll from the Chicago Council on Global Affairs, 42 percent of Americans said the country is less safe than it was before Sept. 11, 2001, compared with 27 percent in a 2014 survey.

Another poll recently conducted by a French polling firm found that nearly of two-thirds of French citizens believed that facts about the 9/11 attacks were being deliberately hidden.