More than 20 U.S. embassies and consulates were shut down Sunday, several days after American officials warned of a possible al-Qaida attack.
Most of those diplomatic missions are in the Muslim world, where Sunday is a regular business day, including embassies in Iraq, Libya and Yemen. U.S. officials say the closures could be extended after an evaluation.
The move came as the U.S. State Department issued a worldwide travel alert to American citizens. The alert said the potential for terrorist attacks is strong in the Middle East and North Africa.
U.S. lawmakers and former high-ranking officials called the decision to close more than 20 diplomatic missions and to issue a global travel alert an extraordinary move.
Other countries took similar actions, and the international police organization Interpol issued its own security alert.
Interpol said its alert stems from recent prison escapes in Iraq, Libya, Pakistan and six other countries. The organization said al-Qaida is suspected of involvement in several of the breakouts.
Britain, Germany and France announced they were closing their embassies in Yemen on Sunday and Monday due to increased security concerns.
The State Department said al-Qaida and its affiliates may focus efforts to conduct attacks between now and the end of August, and that those attacks could come from the Arabian Peninsula.
The U.S. security moves come nearly a year after Islamic militants attacked the U.S. consulate in Benghazi, Libya, killing four Americans including the U.S. ambassador.