Libya has confirmed the US ambassador and three officials have died in a rocket attack in the city of Benghazi.
Christopher Stevens was among those killed in a protest at the US consulate on Tuesday over an American produced film that is said to insult the Prophet Muhammad.
Deputy Prime Minister Mustafa Abu Shagur and deputy minister of the interior Wanis al-Sharif confirmed the deaths.
"I do condemn the cowardly act of attacking the US consulate and the killing of Mr Stevens and the other diplomats," Abu Shagur wrote on Twitter.
The BBC reports that unidentified armed men stormed the grounds, shooting at buildings and throwing handmade bombs into the compound.
Security forces returned fire, but Libyan officials say they were overwhelmed. A Libyan official has said Mr Stevens died from suffocation as a result of the attack, but the exact circumstances remain unclear.
The ambassador had been in Libya for less than four months after taking up his post in the capital Tripoli in May.
The violent protest came hours after thousands of demonstrators gathered outside the US embassy in the Egyptian capital Cairo to express their anger at the film.
Ambassador hailed Libyan revolt
Chris Stevens had hailed the Libyan revolt that overthrew Colonel Muammar Gaddafi.
Mr Stevens had served as envoy to the Libyan rebels from the early weeks of the February 2011 revolt, in which NATO aircraft helped rebels overthrow the 40-year-old regime and eventually capture and kill Gaddafi, AFP reports.
"I was thrilled to watch the Libyan people stand up and demand their rights," he said in a video introduction released by the US State Department shortly after he was appointed ambassador in May this year.
"Now I'm excited to return to Libya to continue the great work we've started, building a solid partnership between the United States and Libya to help you, the Libyan people, achieve your goals."
In the video, Mr Stevens talked about growing up in California and graduating from the University of California at Berkeley.
He described how he fell in love with the Middle East and North Africa during a two-year stint in the Peace Corps, when he worked as an English teacher in Morocco's Atlas Mountains. He went on to join the State Department and serve as a foreign service officer in Jerusalem, Damascus, Cairo and Riyadh.
The Arabic and French-speaking diplomat also served in Libya as deputy chief of mission between 2007 and 2009, shortly after the US restored relations with Gaddafi's regime.
Libya is still being ruled by transitional authorities following the ousting of Gaddafi. The government has only recently been elected and came into power in August this year.