State Department spokesman Mark Toner told reporters Friday that the decision not to keep a DC-3 plane in Tripoli -- and use charter flights, instead, if needed -- "is a very common practice" in places where commercial airline service is available.

In the days after the assault, U.S. administration officials offered conflicting assessments on what may have led to the fatal security breach. Senior State Department officials have maintained that despite significant improvements to security at the post over the past several months, the security personnel in Benghazi were outmanned by several dozen heavily armed extremists during the attack and that no reasonable security presence could have fended off the sustained assault the consulate faced.

Officials initially said the violence erupted spontaneously amid a large protest about a privately made video produced in the United States that mocked the Prophet Mohammed.

But the U.S. intelligence community revised its assessment. It now believes the incident was "a deliberate and organized terrorist assault carried out by extremists" affiliated with or sympathetic to al Qaeda.

For the first time, an FBI team spent "a number of hours" last week at the Benghazi attack site, Pentagon spokesman George Little said. They were accompanied by what Little described as a "small footprint of (U.S.) military personnel."

U.S. Special Operations Forces units have been in Libya, as well as nearby countries, to help collect intelligence about the assault, a U.S. military official told CNN last week. The official declined to be identified due to the sensitive nature of the information.

Officials said the military presence was an indication of ongoing security concerns in the region, which is a major reason why it took FBI agents three weeks to visit the attack site. That gap, however, has raised questions about the integrity of the FBI investigation and concerns that sensitive documents may have been left unsecured.

Three days after the attack, CNN Senior International Correspondent Arwa Damon discovered Stevens' journal during a visit to the unguarded, abandoned compound.

Last week, a Washington Post reporter visiting the site found sensitive documents, including emergency evacuation protocols, details of U.S. weapons collection efforts, and personnel records of Libyans who had been contracted to provide security.

The State Department has said no classified documents had been left on the premises.