The United States is stepping up security measures amid fears that Al-Qaeda might engage in terrorist acts in order to retaliate for Osama bin Laden’s death.

The New York City Police Department sent additional officers to areas around subway stations during commuting hours while port authorities in New York and New Jersey boosted security level for their major facilities.

In Washington, a more-than-usual amount of police officers in full uniform were spotted both inside and outside major subway stations while armed agents were seen keeping watch outside the headquarters of the Central Intelligence Agency.

Homeland Security Secretary Janet Napolitano said authorities were "at a heightened state of vigilance.” However, she was quick to add that the department has no plans to raise its terrorism alert level.