US president Barack Obama has praised a "truly 'United' States" in a speech to commemorate the tenth anniversary of the September 11 terrorist attacks.

The president said that generations to come "will know that nothing can break the will of a truly United States of America".

He added: "They will remember that we have overcome slavery and Civil War, we have overcome bread lines and fascism, and recession and riots, communism and, yes, terrorism."

Al-Qaeda's attacks on New York and Washington killed nearly 3,000 people on September 11 2001. Obama admitted that America would never be the same again in light of the attacks.

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"On September 12, 2001, we awoke to a world in which evil was closer at hand, and uncertainty clouded our future," he said.

"In the decade since, much has changed for Americans. We've known war and recession, passionate debates and political divides.

"We can never get back the lives we lost on that day, or the Americans who made the ultimate sacrifice in the wars that followed."

However, the president stressed that America's spirt had not been broken by the attacks. He cited the country's solid belief in democracy and self-government, and proclaimed: "These past 10 years have shown that America does not give in to fear."

Perhaps surprisingly, Obama even praised his predecessor George Bush's response to 9/11.

"We have not succumbed to suspicion and mistrust. After 9/11, President Bush, to his great credit, made clear what we reaffirm today: the United States will never wage war against Islam or any religion," Obama said.