The United States issued a worldwide alert Friday warning of plans by al-Qaeda to launch an attack in the Middle East or North Africa in August.
The State Department issued the worldwide caution to U.S. citizens a day after announcing that a number of embassies would shut on Sunday as a precaution.
The State Department said attacks were possible "particularly in the Middle East and North Africa, and possibly occurring in or emanating from the Arabian Peninsula."
"Current information suggests that al-Qaeda and affiliated organizations continue to plan terrorist attacks both in the region and beyond, and that they may focus efforts to conduct attacks in the period between now and the end of August," the State Department said in a worldwide travel alert for U.S. citizens.
The alert warned of "the potential for terrorists to attack public transportation systems and other tourist infrastructure."
State Department spokeswoman Marie Harf said earlier that the United States would close a number of embassies and consulates on Sunday, a work day in much of the Islamic world.
She said that some embassies or consulates could decide to remain closed beyond Sunday.
The Arabian Peninsula is the historic base of al-Qaeda, founded by Saudi-born extremist Osama bin Laden who was killed in a U.S. strike in Pakistan in 2011.
The United States has been especially cautious about security since an attack on its consulate in Benghazi, Libya on September 11 last year.
The assault by Islamic extremists in the lawless city killed four Americans, including ambassador Chris Stevens.
U.S. warns of Mideast al-Qaeda threat in August