UPDATE: Foreign Minister Bob Carr has described the killing of a United States diplomat in Libya as a "barbaric attack".
US Ambassador to Libya Christopher Stevens and three of his staff were murdered when armed Islamist extremists stormed the consulate in Benghazi on September 11.
It was not clear whether the assault was timed to coincide with the anniversary of the 9/11 terrorist attack on New York.
The New York Times reported fighters involved in the assault were angry over an American-made video depicting the Prophet Muhammad as a "villainous, homosexual and child-molesting buffoon".
In condemning the attack, Senator Carr also revealed Mr Stevens had played an important role in helping to secure the release of detained Australian lawyer Melinda Taylor earlier this year.
"This was a barbaric attack and it deserves the strongest condemnation," Senator Carr said.
"Ambassador Chris Stevens was a friend to Australia. When we were trying to exert pressure to get Melinda Taylor freed, Chris Stevens was one of the people on the ground in Libya who made representations on our behalf and for her release.
"And he was a diplomat doing his job for his nation - seeking to build bridges between America and the people of Libya."
Senator Carr said the killings, which were confirmed by the US State Department at 10.30pm (AEST) on Wednesday, raised the important issue of protection for foreign diplomats.
He said all diplomats should be "immune from this sort of attack".
"They are unarmed and they are easy targets but the international system is based on the work they do," he said.
Senator Carr said condolences for Ambassador Stevens' death had been passed on to US Secretary of State Hillary Clinton, and US ambassador in Australia Jeffrey Bleich.
He said the attack served to highlight the fragility and complexity of the political situation in Libya.
"The perpetrators of this attack must be brought to justice. And President Magariaf and his Government deserve our support as they seek to do so," he said.
US ambassador killed in Libya
US PRESIDENT Barack Obama has condemned "in the strongest terms" the attack on the US consulate in Libya that left the ambassador and three other American embassy staff dead.
He has ordered tighter security at diplomatic posts across the world and vowed the US will work with the Libyan government to bring to justice those who carried out the attack, which came on the 11th anniversary of the September 11 attacks.
With Secretary of State Hillary Clinton at his side in the White House Rose Garden, Obama paid tribute to US Ambassador Chris Stevens and the others killed in "this terrible act".
"These four Americans stood up for freedom and human dignity," he said.
Violent protests erupted in Libya and Egypt over a film made by an Israeli living in California about the Prophet Muhammad seen as blasphemous by Muslims.
Read more at Brisbane Times