Law enforcement agencies around the U.S. added security measures on Monday following Osama bin Laden's death, out of what one called "an abundance of caution."
In Los Angeles, police were stepping up intelligence monitoring, while New York was sending extra police to its subways, airports, bridges and the World Trade Center site itself.
Judy Banez, a nurse who commutes to New York City from Pennsylvania and lived in Queens on 9/11, said she was happy bin Laden was killed and had no problem with the added security at New York's Port Authority Bus Terminal.
"We're being vigilant and we can now go on with our lives," she said.
The Port Authority of New York and New Jersey said it will add more police at the facilities it runs, which include the airports, the George Washington Bridge and ground zero.
"This response is not based on a current threat, but out of an abundance of caution until we have the chance to learn more," the agency said.
Eighty-four Port Authority employees died in the attack on the World Trade Center on Sept. 11, 2001.
Washington's Metro transit system also stepped up security.
New York Police Commissioner Ray Kelly issued a message to all police commands reminding them that while there's no information indicating a specific threat to the nation's biggest city, officers should remain alert.
He directed that the midnight tour in the subway system be held over into the morning rush-hour.
The head of the House Homeland Security Committee said the U.S. must temper victory with vigilance in the wake of bin Laden's assassination.
Rep. Peter King told NBC's "Today" show the al-Qaida terrorist organization could "try to avenge this death" and said "we'll have to be on full alert."
King also said there will be "round-the-clock" government surveillance to determine if al-Qaida is planning or organizing a retaliatory attack. He said federal agencies will be trying to find out if an attack is possible or imminent, "and how we can prevent it."
In Los Angeles, a top counterterrorism commander said police will be stepping up intelligence monitoring.
Assistant Commanding Officer Blake Chow, who heads the department's counterterrorism and special operations bureau, said Sunday night that officers will be keeping a close ear on intelligence buzz to develop immediate response plans accordingly.
Police in Philadelphia were on heightened alert, checking on mosques and synagogues and stepping up patrols at transportation hubs and historic places, Lt. Raymond J. Evers said.