US Edition Today marks the eighth anniversary of the terrorist attacks on the World Trade Center and the Pentagon on September 11, 2001 that killed nearly 3,000 people in the US.
In preparation, the FBI and Homeland Security Department sent a bulletin to law enforcement agencies nationwide.
The bulletin is similar to past advisories on holidays and other significant dates, and gives no indication of any specific threat.
It reminds police that terrorists in other countries recently have attacked public business sites like hotels.
Richard Kolko, Justice Department spokesman, said issuing the bulletin was routine.
The eight anniversary of the attacks comes amid growing frustration among New Yorkers that little progress has been made on a project to rebuild Ground Zero.
Six and a half years after ambitious and highly symbolic designs were unveiled for the devastated 16-acre site in lower Manhattan, a combination of political wrangling, financial rows, engineering complications and the economic downturn have meant there is little to show for all the talk of standing up to terrorism.
Only one of the five towers planned for the Ground Zero site has broken ground. The frame for the 1,776-foot so-called Freedom Tower is now several stories high but, humiliatingly for some, the landmark building has been renamed One World Trade Centre to make it more marketable to clients.