A suicide bomb goes off at the U.S. Embassy in Ankara, Turkey, on February 1. A security guard was killed and a journalist was wounded in the attack. The Revolutionary People's Liberation Party-Front, or DHKP-C, took responsibility for the bombing. Take a look at other attacks on U.S. diplomatic sites around the world in recent years. 
Demonstrators set the U.S. Consulate compound in Benghazi, Libya, on fire on September 11, 2012. The U.S. ambassador and three other U.S. nationals were killed during the attack. 
People flee the scene of a Taliban attack on the U.S. Embassy in Kabul, Afghanistan, on September 13, 2011. Three police officers and one civilian were killed. There were no reports of U.S. casualties. 
Officials examine the aftermath of a terrorist attack outside the U.S. Consulate in Peshawar, Pakistan, on April 5, 2010. The coordinated attack involved a vehicle suicide bomb and attackers who tried to enter the consulate by using grenades and weapons fire. Two consulate security guards and at least six others were killed. 
Yemeni soldiers carry the coffin of a comrade during a funeral on September 25, 2008, in Sanaa. Heavily armed fighters attacked the U.S. Embassy in Yemen on September 17. A car bomb was detonated, killing 10 Yemeni police and civilians and six attackers. 
Relatives of slain police officers are comforted during a funeral in Istanbul, Turkey, on July 10, 2008, a day after the U.S. Consulate there was attacked. Three police officers and three attackers were killed in what the American ambassador to the country called "an obvious act of terrorism" aimed at the U.S. 
A bomb squad team collects evidence at a construction site where a rocket was launched near the U.S. Embassy in Athens, Greece, on January 12, 2007. The anti-tank missile tore through the embassy, but there were no injuries. 
A car exploded near the U.S. Embassy in Damascus, Syria, on September 12, 2006. Fourteen people were wounded. Syrian authorities killed three attackers and apprehended a suspect outside the building. 
A U.S. diplomat and his driver were among at least four people killed on March 2, 2006, in an apparent suicide attack outside the U.S. Consulate in Karachi, Pakistan. 
An attack on the U.S. Consulate in Jeddah, Saudi Arabia, killed nine people on December 7, 2004. A Saudi group linked to al Qaeda claimed responsibility for the attack. 
A Pakistani police officer stands guard outside the U.S. Consulate in Karachi after a gunman opened fire there on February 28, 2003. Two police officers were killed, and six others, including one civilian, were injured. 
Family members of a victim who was killed by a bomb a day earlier embrace at a hospital in Denpasar, Bali, on October 14, 2002. A series of bombs killed more than 200 people at nightclubs while another attack occurred near the U.S. Consulate on the Indonesian tourist island. Authorities believe the attacks were coordinated. 
A previously unknown militant group called Al-Qanoon claimed responsibility for a bombing that killed 10 people at the U.S. Consulate in Karachi, Pakistan, on June 14, 2002. The U.S. State Department says it suspects al Qaeda is responsible. 
Police officers stand next to the body of a victim after a car bomb exploded on March 20, 2002, at a shopping center near the U.S. Embassy in Lima, Peru, killing nine people. 
Christopher Sandrolini, the U.S. consul general in Calcutta, speaks with Indian officials outside the U.S. government information center in Calcutta, near the U.S. Consulate, where heavily armed gunmen killed five Indian police officers on January 22, 2002. 
Rescue workers stand on the remains of a building in front of the U.S. Embassy in Nairobi, Kenya, on August 10, 1998, four days after a deadly attack. Twelve Americans were among more than 200 people killed in nearly simultaneous bombings at U.S. embassies in Nairobi and Dar es Salaam, Tanzania. 
Secretary of State Madeleine Albright, center, walks past the damaged U.S. Embassy in Dar es Salaam on August 18, 1998. The August 7 attacks in Tanzania and Kenya were later attributed to al Qaeda. 
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- Bergen, Cahall: U.S. issued global travel alert, 21 embassies, consulates close Aug. 4
- That day is Ramadan 'Night of Power,' also seen by al Qaeda as good night for martyrdom
- They say night of power has brought earlier terror attacks; embassies a favored target
- Writers: Target may be Egypt, where earlier attack aimed; jailbreaks may also be factor
Editor's note: Peter Bergen is CNN's national security analyst, a director at the New America Foundation and the author of "Manhunt: The Ten-Year Search for bin Laden -- From 9/11 to Abbottabad." Bailey Cahall is a research associate at the New America Foundation.
(CNN) -- On Friday the U.S. State Department issued a worldwide travel alert because of an unspecified al Qaeda threat. The location of that threat, the department said in a bulletin, is "particularly in the Middle East and North Africa, and possibly occurring in or emanating from the Arabian Peninsula." As a result, an unprecedented 21 embassies and consulates in 17 countries in the Middle East, North Africa and South Asia will close on Sunday.
Sunday is also the 27th day of Ramadan and a particularly holy day for the world's Muslims as it is the "Night of Power," when the first verses of the Koran were revealed to the Prophet Mohammed.
It is also seen by al Qaeda's would-be martyrs as a particularly auspicious day to die.
On the Night of Power in 2000, which that year fell on January 3, al Qaeda militants attempted to launch a suicide attack against the American warship USS The Sullivans off the coast of Yemen with a bomb-filled boat.
That attack failed, but the same group of militants then attacked the USS Cole 10 months later, again using the tactic of a bomb-laden boat, which exploded, killing 17 American sailors.
It was the day after the Night of Power in December 2001 that Osama bin Laden signed his will as he feared death from American bombs falling during the battle of Tora Bora in eastern Afghanistan.
Al Qaeda and aligned organizations have a long history of attacking U.S. embassies and consulates, beginning in 1998 with the bombings of the embassies in Tanzania and Kenya, which killed more than 200, and including, most recently, the storming of the U.S. government facility in Benghazi, Libya, on the 11th anniversary of 9/11 last year.
For al Qaeda, these diplomatic compounds are attractive targets because they symbolize American power and because their locations are widely known. Indeed, several of the embassies and consulates that are being closed on Sunday have been attacked by al Qaeda and affiliated groups before.
Chaffetz: Security measures go too far 
Embassy terror threat 
Terror threat prompts embassy closures In Saudi Arabia, al Qaeda terrorists stormed the U.S. Embassy compound in Riyadh on May 12, 2003, killing 36 people. A year-and-a-half later, militants breached the outer wall of the U.S. consulate in Jeddah and opened fire on the staff, killing five.
The U.S. embassy in Sana'a, Yemen, was targeted by an al Qaeda affiliate two times in 2008, attacks that killed 21.
On September 13, 2011, the Haqqani network, a Taliban group closely associated with al Qaeda, attacked the U.S. Embassy in Kabul, killing five Afghan police officers and 11 civilians.
Though U.S. officials have not confirmed the targeting of a specific embassy, it is likely that the American compound in Cairo is a particular point of concern. In May, three men were arrested by Egyptian officials, who said the men were planning to attack the embassy. Officials said they discovered 22 pounds of aluminum nitrate, instructions on how to make bombs, and materials published by al Qaeda in the Islamic Maghreb, the network's North African affiliate.
Another possible factor in the timing of the al Qaeda alert is that in the past two weeks, massive jailbreaks in Iraq and Libya have released more than a thousand prisoners, some with significant ties to al Qaeda. Very few of those inmates have been recaptured.
The U.S. embassies in Baghdad, Iraq, and Tripoli, Libya, are among the facilities that will be closed on Sunday.
(Note: An earlier version of this story misstated the timing of Osama bin Laden's will signing.)
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