President Barack Obama said on Saturday the US was stronger 10 years after the Sept 11, 2001, attacks and Americans would "carry on" despite continued threats against their safety.

Marking Sunday's 10th anniversary of the "9/11" attacks on New York, Washington and Pennsylvania, Obama noted that al Qaeda's strength had been sapped by relentless US efforts in the decade since the tragedy killed nearly 3,000 people.

"Thanks to the tireless efforts of our military personnel and our intelligence, law enforcement and homeland security professionals, there should be no doubt: today, America is stronger and al Qaeda is on the path to defeat," Obama said in his weekly radio and Internet address.

New York police amassed a display of force on Friday, including checkpoints that snarled traffic in response to intelligence about a car or truck bomb plot linked to the anniversary.

Obama noted that terror groups would continue to target the US. "Yes we face a determined foe, and make no mistake -- they will keep trying to hit us again. But as we are showing again this weekend, we remain vigilant," he said.

"We're doing everything in our power to protect our people, and no matter what comes our way, as a resilient nation, we will carry on."

Rudolph Giuliani, the mayor of New York at the time of the attacks, said the country still had work to do to become better prepared for further threats.

"People often ask me, 'Is America safer now than it was before September 11?' The answer is: 'Yes, but not as safe as we should be,'" he said in the weekly Republican address.

"We've made significant improvements in intelligence gathering and in airport security. But much work remains," he said, citing port security and preparedness levels at state and local governments as requiring improvement.

Obama will travel to all three sites on Sunday where hijackers turned planes into missiles, bringing down the twin towers of the World Trade Center in New York, hitting the Pentagon in Virginia and crashing into a Pennsylvania field.

The attacks sparked US-led wars in Afghanistan and Iraq, the latter of which Obama, a Democrat, opposed.

"They wanted to draw us in to endless wars, sapping our strength and confidence as a nation. But even as we put relentless pressure on al Qaeda, we're ending the war in Iraq and beginning to bring our troops home from Afghanistan," he said.

"Because after a hard decade of war, it is time for nation building here at home."

Giuliani, who made a failed bid for the 2008 Republican presidential nomination, said the attacks showed the importance of a US military presence abroad, and he indicated he opposed a hasty withdrawal of forces from those two war zones.

"The (drawdown) timetable should not be based on a politically expedient calendar, but on when we've eliminated the threat of domestic attacks being generated in that particular part of the world," he said.

"We must not allow impatience to prevent our military from achieving its objective in Iraq and Afghanistan -- and the objective is the elimination of the threat to our nation."

US forces killed former al Qaeda leader Osama bin Laden, considered the mastermind of the September 11 attacks, earlier this year. The president referred to bin Laden's death and said the democratic movements in Arab countries cast a shadow over al Qaeda's legacy.

"We've forged new partnerships with nations around the world to meet the global challenges that no nation can face alone," Obama said.

"And across the Middle East and North Africa, a new generation of citizens is showing that the future belongs to those that want to build, not destroy," he added.-Reuters