Tripoli - Libya has set up an independent judicial committee to probe an attack on the US consulate in Benghazi in which four Americans including the ambassador were killed, a spokesperson said on Thursday.
"All measures are being taken. An independent judicial committee has been set up to carry out an inquiry," Abdelmonem al-Horr, spokesperson for the Libyan interior ministry's security commission, told AFP.
Asked whether any arrests were expected, Horr replied "Obviously", but did not elaborate.
Tuesday's assault on the consulate was initially believed to have been motivated by outrage over an amateur internet film made in America that insulted Islam, but US officials later said it might have been a planned, pre-meditated assault by al-Qaeda affiliates or sympathisers.
It began when a mob stormed the consulate but later, according to witnesses, armed hardliners aimed rocket-propelled grenades at the complex before setting it alight, killing US Ambassador Chris Stevens and three other Americans.
According to Horr, the inquiry will be "very complicated" due to the fact that the crowd which had gathered outside the consulate had been very mixed.
"There were extremists, ordinary citizens, women, children and criminals," he said.
"There were also shots fired from a nearby farm. We need time to determine who was responsible."
Libya has apologised to the United States over the attack, which was discussed in a telephone conversation between US President Barack Obama and Mohamed al-Megaryef, president of Libya's highest political authority the General National Congress.
US officials said Obama thanked Megaryef for expressing condolences while urging Libya to work with US authorities to bring those behind the deadly attack to justice.
"He also expressed appreciation for the co-operation we have received from the Libyan government and people in responding to this outrageous attack, and said that the Libyan government must continue to work with us to assure the security of our personnel," the White House said in a statement.
"The President made it clear that we must work together to do whatever is necessary to identify the perpetrators of this attack and bring them to justice," it said.
The United States had earlier dispatched navy destroyers and Marines to Libya in the aftermath of the attack.