The attackers failed to breach the compound's walls, and none of those killed or wounded were U.S. diplomats or embassy employees. But the assault was well-coordinated and more sophisticated than previous attacks on the mission, involving two suicide car bombs and a team of well-armed gunmen that managed to penetrate rings of security right to one of the embassy entrances.
In the sweep after the attack, 25 militants were rounded up from various parts of Yemen over 24 hours and were being questioned by Yemeni and U.S. investigators, the Yemeni security official said, speaking on condition of anonymity because he was not authorized to give details.
It is not unusual for authorities in Yemen, a key partner in the U.S.-led war on terror but for years an al-Qaida stronghold, to round up a large number of suspects after a terror attack. The official said a U.S. team, possibly from the FBI, was on its way to Yemen to take charge of the investigation. A U.S. Embassy official would not confirm the dispatch of an FBI team.
An Associated Press reporter who visited the embassy Thursday saw a group of non-Yemeni men investigating the damage caused by the attack outside the embassy's large walls. The men were sifting through the debris, plastering what appeared to be white tags on several objects scattered on the ground.
The reporter could also see pieces of what appeared to be human flesh outside the walls, which were pockmarked and stained with blood. There were also a small crater just outside the walls and at least a dozen badly damaged cars, with their windows missing and tires melted.
In Washington, the State Department issued a travel warning, asking American citizens to "defer nonessential travel" to Yemen. The U.S. also authorized -- but did not order -- the departure of the non-emergency embassy personnel. U.S. embassies in other Arab Gulf countries put out advisories warning Americans to "remain alert to personal security."
The assault began at 9:15 on Wednesday, when militants -- some dressed in army uniforms and armed with rocket-propelled grenades and automatic weapons -- attacked Yemeni guards at a checkpoint on the street outside the embassy.
Amid the gunbattle, a suicide car bomb struck a guard post near the embassy's main gate, U.S. State Department spokesman Sean McCormack said. "It did not reach the actual entrance to the embassy" and did not breach the wall, he told reporters in Washington. Moments later, a second car bomb struck near a pedestrian entrance to the compound nearby, he said.
The embassy building, a Western-style villa, stands around 100 yards beyond the entrances within the walls and so was not damaged. But civilians waiting in line for visas outside the embassy were among the casualties.
Six attackers, six Yemeni guards and four civilians were killed. A fifth civilian -- a 30-year-old Yemeni who lived in a residential area nearby -- died later, Yemeni security officials said, also speaking on condition of anonymity because they were not authorized to talk to the press.
Among the civilian dead was Susan Elbaneh, 18, an American from Lackawanna, N.Y., and her Yemeni husband, who her family said had been recently wed in an arranged marriage. They were apparently at the embassy to do paperwork for the husband's move to the U.S. when the attackers struck, said Elbaneh's brother, Ahmed. The State Department confirmed the deaths Thursday.
President Bush called the attack "a reminder that we are at war with extremists who will murder innocent people to achieve their ideological objectives."
The U.S. counts Yemen as an ally in the war on terrorism. But American officials have long been frustrated over what is seen as a "revolving door" policy toward al-Qaida militants by President Ali Abdullah Saleh's government.
Yemen has let some convicted militants go free after promising to refrain from violence.
In 2006, a group of 23 militants escaped from a high-security prison, including 10 figures convicted in al-Qaida's 2000 bombing of the USS Cole destroyer in Aden harbor. There were widespread reports of security officials' collusion in the escape, and experts say Yemen's security and intelligence services are riddled with militant sympathizers.
State control is weak in the impoverished country -- the ancestral homeland of Osama bin Laden -- tribes are strong and many mountainous rural areas are lawless, giving ample room for militant training camps.
The U.S. Embassy has been attacked four times since 2003, most recently in March when a volley of mortars targeting the compound hit a neighboring girls high school instead, killing a Yemeni guard and wounding dozens of girls.
There has not been a public claim of responsibility for the attack. Some Yemeni security officials said a local militant group called Islamic Jihad, which Yemeni authorities have cracked down on previously, claimed responsibility. But Yemeni authorities have blamed the group in past attacks that have later been claimed by al-Qaida.
The group is unrelated to the Palestinian group of the same name.
Suspicion about Wednesday's attack was immediately centered on al-Qaida, which has long operated in the country on the southern tip of the Arabian peninsula.
Yemen has been a focus of American counterterrorism efforts ever since the 2000 Cole attack, in which 17 American sailors were killed by suicide bombers on a boat. A similar attack two years later hit a French oil tanker, killing one person. Since that attack and the Sept. 11 attacks, Yemen has been cracking down on militants, earning praise from Washington.
Associated Press writer Carolyn Thompson contributed to this report from Lackawanna, N.Y.