A ‘big advance’ has been made in the probe into the deadly attack on the US consulate in Libya's second city Benghazi that killed four Americans in Libya, including the U.S. ambassador, Prime Minister Mustafa Abu Shagur said in an exclusive interview on Thursday.

"We have made a big advance," Abu Shagur said in his first interview since his election as premier on Wednesday night.

"We have some names and some photographs. Arrests have been made and more are under way as we speak."

The new prime minister did not elaborate on how many suspects were in custody or what groups, if any, they were connected to. "We don't want to categorise these people until we know all the facts," he said.

Organised attack

A senior security official says the attack was an organised two-part operation by heavily armed militants that included a precisely timed raid on a supposedly secret safe house just as Libyan and U.S. security forces were arriving to rescue evacuated consulate staff.

Wanis al-Sharef, eastern Libya's deputy interior minister, said on Thursday the attacks were suspected to have been timed to mark the 9/11 anniversary and that the militants used civilians protesting an anti-Islam film as cover for their action.

He said Ambassador Chris Stevens and another American were killed in the consulate as plainclothes Libyan security were evacuating them to the safe house. The second assault targeted the safe house, killing two Americans and wounding nearly about 30 Libyans and Americans.

He was reticent about going into details when he spoke to media earlier Thursday.

"The interior and justice ministries have begun their investigations and evidence gathering and some people have been arrested," he said.

He declined to give any details of the number of people in custody or their backgrounds ‘so as not to hamper the smooth running of the investigation’.

Ambassador dies of suffocation?

Initial reports said Ambassador Chris Stevens and three other Americans were killed by a mob outside the consulate in the eastern city of Benghazi on Tuesday as they tried to flee an angry protest against a US-produced movie deemed offensive to Islam.

But it is now believed Stevens died from smoke inhalation after becoming trapped in the compound when suspected Islamic militants fired on the building with rocket-propelled grenades and set it ablaze.

Al-Qaeda has a role?

US officials are investigating the possibility that the assault was a plot by Al-Qaeda affiliates or sympathisers, using the protest against the film as a cover to carry out a coordinated revenge attack on Tuesday's anniversary of the September 11, 2001 attacks in the United States.

Libyan authorities initially pointed a finger of blame at supporters of Moamer Kadhafi, who was ousted and slain in an uprising last year that was backed by NATO air power, and at Al-Qaeda.

But Abu Shagur played down the Al-Qaeda line.

"We don't have any proof as yet of an Al-Qaeda presence as an organisation in Libya," although "some youths have been influenced by the extremist ideology of Al-Qaeda," he said.

Abu Shagur said extremists were a tiny minority in Libya who 'do not number more than 100 or 150', whereas most young Islamists in the country were moderates.

The attack on the US consulate was ‘a cowardly, criminal and terrorist act’, he said, adding it was ‘isolated, not representing a phenomenon in Libyan society and it will not have negative consequences with our allies’ who backed the revolution.

He did not have confirmation that the United States was sending two warships off the Libyan coast. "But we will not accept anyone entering inside Libya. That would infringe on sovereignty and we will refuse," the premier said.

A decision to deploy a team of 50 US Marines was taken ‘in coordination with Libyan authorities’, he added. They would guard the US embassy in Tripoli and two diplomatic residences.

Hardline Sunni Islamists of the Salafist group Katibat Ansar al-Sharia (Brigade of the Supporters of Sharia) have also been blamed for the Benghazi attack.

But in a statement on Thursday, the group condemned ‘the accusations without any verification or investigation’ which had emerged against it in the Libyan media.