President Barack Obama has ordered that "all appropriate steps" be taken to protect Americans in response to a threat of an al-Qaeda attack, a White House official said on Friday.
"The president is being updated on a potential threat occurring in or emanating from the Arabian Peninsula," the official said on condition of anonymity.
One day after announcing it would close a number of embassies across the Islamic world on Sunday, the US State Department issued a worldwide warning that al-Qaeda may attack in August.
It said attacks were possible "particularly in the Middle East and North Africa, and possibly occurring in or emanating from the Arabian Peninsula."
"The State Department's newly-released travel alert makes clear that al-Qaeda and affiliated organizations continue to plan terrorist attacks both in the region and beyond," the official said.
Obama "will continue to be updated on a regular basis" on the threat and related developments, the official added.