"Given the uncertainty and volatility of the current situation, US citizens in areas where events could cause anti-American violence are strongly urged to limit their travel outside of their homes and hotels and avoid mass gatherings and demonstrations," the State Department said in a statement.
President Barack Obama warned Americans Sunday night to remain vigilant even after the killing of al Qaeda leader Osama bin Laden and while there are no known credible threats, the risk of attacks remains.
The Department of Homeland Security (DHS) and the FBI have not issued any warning of a credible or imminent threat in the wake of news that bin Laden was killed in Pakistan, but security will likely be ramped up to guard against possible retaliation.
"There is no doubt that al Qaeda will continue to pursue attacks against us. We must and we will remain vigilant at home and abroad," Obama said in a late-night televised statement announcing that US forces had killed bin Laden.
bin Laden's death is a major milestone for the U.S., but its precise effects on the battle against terrorism are unclear. Although bin Laden is the inspirational leader of al Qaeda and its offshoots around the world, he isn't thought to be a critical operational leader of the organization. Increasingly, terrorist actions have been undertaken by offshoots of his organization.
But bin Laden remained the worldwide symbol of the terrorist network and militant Islam more broadly. His death will be a major blow to al Qaeda, and one that makes the organization look less powerful.
"Taliban fighters have an admiration for Osama. It will affect their morale" and trigger retaliatory attacks, a Taliban commander in Paktia province in Afghanistan said in a phone interview.
The U.S. believes that Mr. bin Laden will be succeeded by his longtime No. 2, Ayman el Zawahiri. According to a senior administration official, el Zawahiri is "far less charismatic and not as well respected" as bin Laden within the organization and will likely have "difficulty" maintaining the loyalty of bin Laden's largely Gulf Arab followers.