Libya's interim president, Mohammed el-Megarif, apologized over the killing of Stevens and three other US personnel on Tuesday night. During a mob attack on the compound, gunmen fired rockets in Stevens' direction, said Libyan officials.

"We extend our apology to America, the American people and the whole world," President el-Megarif said. "While we vehemently condemn any attempt to defame our prophet, we strongly denounce any use of force and the killing of innocents."

Libya admits not prepared

Libyan Supreme Security Committee spokesman Abdel-Monen Al-Hurr said Libyan security guards in Benghazi were "not prepared for the intensity of the attack."

Deputy Interior Minister Wanis Al-Sharif said two of the US personnel were killed during a shootout when militants located consular staff, after they had shifted to a safe house nearby. Between 12 and 17 others were wounded, he added.

US sources quoted by several news agencies said on Wednesday that 50 specialist anti-terrorism Marines were being sent to Libya to reinforce security at US facilities.

Outrageous, Obama says

In Washington, US President Barack Obama said "the US condemns in the strongest terms this outrageous attack," which came a year after the ouster of Libya's slain dictator Moammar Gadhafi.

"Make no mistake, we will work with the Libyan government to bring to justice the killers who attacked our people," Obama said, while noting that the Benghazi attack had taken place 11 years to the day since al Qaeda hijackers toppled the World Trade Center in New York City.

The attack in Benghazi would "not break the bounds between the US and Libya," Obama said, adding that Stevens had "worked tirelessly to support this young democracy."

Savage extremists, Clinton says

US Secretary of State Hillary Clinton said those who killed Stevens were a "small and savage group, not the people or government of Libya." America would continue its work to help stabilize Libya, she said.

"A free and stable Libya is still in America's interests. We will not turn our backs on that," Clinton said.

"As the conflict in Libya unfolded, Chris was one of the first Americans on the ground in Benghazi," Clinton said. "He risked his own life to lend the Libyan people a helping hand to build the foundation for a new, free nation."

EU calls attack despicable

From Brussels, EU foreign policy chief Catherine Ashton described Tuesday's Benghazi attack as "despicable."

She called on Libyan authorities "to take all necessary measures without delay to protect the lives of all diplomats and foreign staff" working to restore peace in Libya.

From Strasbourg, European Parliament chairman Martin Schulz, a German Social Democrat, urged Libya to find the perpetrators and bring them to justice.

From Berlin, German government spokesman Steffen Seibert said Stevens and his aides had been the "victims of this religious fanaticism which does not preserve human life."

Five-year stint in Libya

Stevens, a former California-trained lawyer, had been the US ambassador to Libya since May 22. He had arrived in 2007 and first served as deputy chief of mission. In March last year as Gadhafi cracked down on rebels, Stevens became special US envoy to the Libya's opposition as NATO conducted a decisive aerial campaign.

Security experts say Libya's government has struggled to impose its authority over numerous Islamist militant groups around Benghazi. The eastern Libyan city was a major rebel base during last year's uprising against Gadhafi.

ipj/jr (AP, Reuters, AFP, dpa)