Australia lost a good friend when U.S. Ambassador to Libya Christopher Stevens was killed Tuesday during what appeared as spontaneous 'mob attack', Foreign Minister Bob Carr said on Thursday.

In a statement, Senator Carr lamented that the American diplomat, who served in Libya while the revolution against strongman Muammar Gaddafi was raging last year, was slain while "doing his job for his nation - seeking to build bridges between America and the people of Libya."

Condolences from Canberra, he added, have been transmitted U.S. Secretary of State Hillary Clinton.

"Libya is a country finding its way out of the wreckage of decades of dictatorship ... and this attack from the political sidelines is a reminder that the politics of Libya are complex and fragile," Fairfax reported Senator Carr as saying today.

He also joined calls by the international community that those responsible for the assault on the U.S. consular office in Benghazi, which also killed three other American consulate officials, be brought to justice.

What happened this week, Senator Carr said, highlighted the risks face by diplomats in performing their duties, adding that since they "are easy targets ... (they) should be protected and should be immune from this sort of attack."

Mr Stevens, according to the foreign minister, was instrumental in the efforts that won the release of Australian lawyer Melinda Taylor earlier this year.

"Chris Stevens was one of the people on the ground in Libya who made representations on our behalf and for her release," Senator Carr said in his statement.

Meanwhile, U.S President Barack Obama condemned the attack and vowed that the perpetrators would be tracked down by U.S forces. Already, an elite team of U.S Marines has been dispatched to the North African nation to help secure American personnel and undertake evacuation when necessary, Reuters reported.

Washington is also looking into suggestions that the mob attack was actually pre-meditated, as reported by CNN, instead of what was first believed as protest actions against the short film 'The Innocence of Muslims' posted on YouTube.

"It bears the hallmarks of an organized attack," one U.S. official was quoted by Reuters as saying.

Speculations also whirled that the incident was timed with the 11th anniversary of the 9/11 attack and likely involved al Qaeda-linked Islamist militants in the region.

The Libyan government has denounced the attack and labelled it as an assault not only against the U.S. government but also of Libya and its people, CNN said in a report on Wednesday.