Washington: Ahead of tenth anniversary of 9/11 attacks, President Barack Obama has asked Americans to show unity as the country faces ‘great challenges’.

"On this 10th anniversary, we still face great challenges as a nation. We're emerging from the worst economic crisis in our lifetimes," Obama said in his weekly address to the nation.

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"We're taking the fight to al-Qaeda, ending the war in Iraq and starting to bring our troops home from Afghanistan. We are working to rebuild the foundation of our national strength here at home. None of this will be easy," he said.

Obama asked Americans to come together in the spirit of service and remembrance of those who lost their lives in the terrorist attack 10 years ago.

"In just two weeks, we'll come together, as a nation, to mark the 10th anniversary of the September 11th attacks. We'll remember the innocent lives we lost. We'll stand with the families who loved them," Obama said.

"And it can't be the work of government alone. As we saw after 9/11, the strength of America has always been the character and compassion of our people. So as we mark this solemn anniversary, let's summon that spirit once more.

And let's show that the sense of common purpose that we need in America doesn't have to be a fleeting moment; it can be a lasting virtue—not just on one day, but every day," Obama said.

We'll honour the heroic first responders who rushed to the scene and saved so many and we'll pay tribute to our troops and military families, and all those who have served over the past ten years, to keep us safe and strong, he said.

"We'll also recall how the worst terrorist attack in American history brought out the best in the American people."