The US government is investigating whether al-Qaeda-linked extremists were behind Tuesday night's raid, rather than simply a spontaneous mob of protesters.
The Libyan government announced the first arrests over the Benghazi consulate attack on Thursday as suspicion focused on two militant Islamist groups in the area.
Mustafa Abu Shagur, the Libyan prime minister, said "a big advance" had been made in the inquiry, though he refused to give specific details. Wanis Sharif, the deputy interior minister, later said four arrests had been made.
The US government is investigating whether al-Qaeda-linked extremists were behind Tuesday night's raid, rather than simply a spontaneous mob of protesters.
That suggestion strengthened yesterday when Libyan officials said a farm near the consulate had been used as a base to launch some of the attacks.
President Barack Obama has dispatched 50 US marines and two warships to the region, while Eric Holder, the US attorney general, confirmed that the FBI would help with the investigation.
Last night, Shagur said the Libyan authorities had made a breakthrough, announcing that the first suspects had been arrested. "We have some names and some photographs. Arrests have been made and more are under way as we speak," he said.
A Libyan interior ministry spokesman warned that the inquiry would be "complicated" because the crowd 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."
Ahmad Jibril, the Libyan deputy ambassador in London, has named the group Ansar al-Sharia, which translates as Protectors of the Islamic Law, as the perpetrators of the attack.
"The group has carried out several terrorist attacks within the last few weeks and also the killing of some Libyan officials, especially in Benghazi," he said.
Ansar is led by Mohammed Zahawi and emerged during the uprising against Col Muammar Gaddafi.
After the attack on Tuesday it issued a statement that was neither a denial nor a claim of responsibility. It said the group "didn't participate as a sole entity", but it "was carrying out its duties in al-Jala'a hospital and other places where it was entrusted with some duties".
In a statement yesterday it sought to distance itself from the attacks, condemning "the accusations without any verification or investigation".
The other group that has come into focus is the Imprisoned Omar Abdul Rahman Brigade, named after the "blind sheikh" jailed in the US for conspiracy in the bombing of the New York World Trade Centre in 1993.
){kind=small}
){kind=small}
){kind=small}
){kind=small}
){kind=small}
){kind=small}
){kind=small}
){kind=small}
){kind=small}
){kind=small}
){kind=small}
){kind=small}
){kind=small}
){kind=small}
){kind=small}
){kind=small}
){kind=small}
){kind=small}
){kind=small}
){kind=small}
){kind=small}
){kind=small}
)
){kind=small}
){kind=small}
)
)
)
)
)
){kind=small}
){kind=small}
){kind=small}
){kind=small}
){kind=small}