The U.S. State Department has put its embassies on alert and warned that Americans abroad could be the target of attacks by al Qaeda forces likely disillusioned and recharged by the assassination of their historic leader Osama bin Laden.

In his speech on Sunday night, President Barack Obama did not explain how the battle to stamp out al Qaeda's worldwide network would continue in the coming months.

The State Department said there is "enhanced potential for anti-American violence given recent counterterrorism activity in Pakistan."