The Marines, sent from a base in Spain, were headed initially to the U.S. Embassy in Tripoli, not to Benghazi, according to U.S. officials, who spoke on the condition of anonymity because they were not authorized to talk to the press.
The consulate attack illustrated the breakdown in security in Libya, where the government is still trying to establish authority months after Gadhafi's fall.
There also were indications that two distinct attacks took place — one on the consulate, then a second hours later early Wednesday on a nearby house to which the staff had been evacuated.
The crowd of several thousand that descended on the consulate was armed with machine guns and rocket-propelled grenades, said Wanis el-Sharef, the deputy interior minister of Libya's eastern region.
A small contingent of Libyan security protecting the facility fired in the air, trying to intimidate the mob. But faced with superior size and firepower, the Libyan security withdrew, el-Sharef said. Gunmen stormed the building, looted its contents and torched it, he said.
Details of how the Americans were killed were still unclear.
Stevens, 52, and a consulate staffer who had stayed behind in the building died in the initial attack, el-Sharef said. The rest of the staff successfully evacuated to a nearby building, preparing to move to Benghazi Airport after daybreak to fly to the capital of Tripoli, he said.
Hours after the storming of the consulate, a separate group of gunmen attacked the other building, opening fire on the more than 30 Americans and Libyans inside. Two more Americans were killed, he said.
Dr. Ziad Abu Zeid, who treated Stevens, told The Associated Press that he died of asphyxiation, apparently from smoke. In a sign of the chaos, Stevens was brought by Libyans to the Benghazi Medical Center with no other Americans, and no one at the facility knew who he was, Abu Zeid said.
He said he tried to revive Stevens for about 90 minutes "with no success." The ambassador was bleeding in his stomach because of the asphyxiation but had no other injuries, the doctor said.
Widely regarded as one of the most effective American envoys to the Arab world, Stevens brokered tribal disputes and conducted U.S. outreach efforts in Jerusalem, Cairo, Damascus and Riyadh. As a rising star in U.S. foreign policy, he retuned to Libya four months ago, determined to see a democracy rise where Gadhafi's dictatorship flourished for four decades.
Smith, 34, was an Air Force veteran who had worked as an information management officer for 10 years in posts such as Brussels, Baghdad and Pretoria. Smith was also well-known in the video game community.
The bloodshed stunned many Libyans, especially since Stevens was a popular envoy among different factions and politicians, including Islamists, and was seen as a supporter of their uprising against Gadhafi.
The leader of Ansar al-Shariah, an armed ultraconservative Islamist group, denied any involvement in the attack.
"We never approve of killing civilians, especially those who helped us," Youssef Jihani said in a reference to Stevens. "We are well-educated and religious."
The violence in Libya raised worries that further protests could break out around the Muslim world, but the reaction was limited.
The two-hour movie that sparked the Cairo protests, titled "Innocence of Muslims," came to attention in Egypt after its trailer was dubbed into Arabic and posted on YouTube. The video-sharing website blocked access to it Wednesday. The trailer depicts Muhammad as a fraud, a womanizer and a madman in an overtly ridiculing way, showing him having sex and calling for massacres.
In Cairo, some 200 Islamists staged a second day of protest outside the U.S. Embassy on Wednesday, but there were no more attempts to scale the embassy walls. After nightfall, the group dwindled and some protesters scuffled with police, who fired tear gas and dispersed them, emptying the streets.
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