WASHINGTON, September 11, 2011 (AFP) - US President Barack Obama said in an interview broadcast amid September 11 commemorations Sunday to look out for suspicious activity as authorities tracked a credible terror threat.

Obama said in an interview with NBC News that US intelligence and security officials had been preparing for months for the 10th anniversary of the Al-Qaeda attack on New York and Washington.

"That doesn't mean though we shouldn't be vigilant," Obama said.

"What we want all Americans to know is, your government has prepared for it."

"It is important for you to keep your eyes open. You should go about doing what you were planning to do on 9/11 anyway.

"But people should be on the lookout and make sure that if something suspicious is taking place you are informing your local law enforcement."

US security agencies have scrambled to chase down what officials said was a credible but unconfirmed threat reportedly received by US intelligence agents this week of an Al-Qaeda attack -- possibly a car bomb in Washington or New York -- around the September 11 commemorations.

Intense security was in place around memorial ceremonies in at the Ground Zero site of the toppled World Trade Center Twin Towers in New York, at the Pentagon near Washington and in Shanksville, Pennsylvania, the crash site of a hijacked airliner brought down by passengers.

During the same interview, Obama recalled September 11, 2001 as a day when a tried and tested United States "came together" in the face of disaster.

"For me, like for most of us, our first reaction was and continues to be just heartbreak for the families involved," Obama told NBC.

"The other thing that we all remember is how America came together, and so 10 years later, I'd say America came through this thing in a way that was consistent with our character," the president said in the interview broadcast Saturday..

"We made mistakes. Some things haven't happened as quickly as they needed to, but overall we took the fight to Al-Qaeda," he added.

"We preserved our values. We preserved our character," he said in the interview at the White House.