Washington (CNN) -- Three weeks after four Americans were killed in an attack on the U.S. Consulate in eastern Libya, an FBI team arrived at the site as the investigation continued in other places, too, a Pentagon spokesman said Thursday.
"You should not assume that all we could do or have been doing is restricted solely to Benghazi," Attorney General Eric Holder told reporters in Washington. "There are a variety of other places in country and outside the country where relevant things could be done and have been done. This is a matter that's been under active investigation almost since the time of the incident and I'm satisfied with the progress that we have made."
Holder said the focus of the Justice Department was "to solve this matter, to hold people accountable. So that's what we will do."
Pentagon spokesman George Little said Thursday that a U.S. military support mission accompanied the FBI team, which was in Benghazi "for a number of hours" before it left the city.
"We have not been sitting around waiting, you know, for information to come to us," Little said, adding that U.S. investigators were "actively chasing leads in various ways."
U.S. Special Operations forces were in Libya and nearby countries aiding in the collection of intelligence regarding the assault, a U.S. military official told CNN Thursday. The official declined to be identified due to the sensitive nature of the information.
The September 11 consulate attack killed U.S. Ambassador to Libya J. Christopher Stevens and three other Americans. The incident heightened global scrutiny of the North African nation and sparked debate over whether the Obama administration has been forthcoming about the incident.
Officials said the military presence was an indication of ongoing security concerns in the region.
Security concerns at the site had led the FBI to delay for more than three weeks its visit to Benghazi. FBI and military officials had cited the need for proper military protection in the event of another attack.
Little described the security team accompanying the FBI as a "small footprint of military personnel."
The visit took place after the Libyans approved the presence of the FBI and the U.S. military in Benghazi.
The U.S. military force that provided security was approved by Libyan government, Little said.
Kevin Perkins, FBI associate deputy director, told a congressional hearing on September 19 that a "significant number of FBI agents, analysts and various support employees" had been assigned to the case.
"We are conducting interviews, gathering evidence and trying to sort out the facts, working with our partners both from a criminal standpoint, as well as in the intelligence community, to try to determine exactly what took place on the ground that evening," he told the Senate Committee on Homeland Security and Government Affairs.
The failure of investigators to visit the site in the immediate aftermath of the attack 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 Correspondent Arwa Damon discovered Stevens' journal during a visit to the unguarded, abandoned compound.
This week, a Washington Post reporter visiting the site found sensitive documents, including personnel records of Libyans who had been contracted to provide security, emergency evacuation protocols and details of U.S. weapons collection efforts.
But a State Department official told CNN that no classified documents had been left on the premises.
In the days after the assault, U.S. administration officials offered conflicting assessments as what may have led to the fatal security breach.
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, saying it believes it was a planned terrorist assault.
The intelligence community now believes it was "a deliberate and organized terrorist assault carried out by extremists" affiliated with or sympathetic to al Qaeda.
Defense Secretary Leon Panetta has said the attack was "clearly" planned and conducted by terrorists, and that it "took a while" for there to be information to reach such a conclusion.
But a senior U.S. official told CNN that, within a day or so of the attack, the U.S. intelligence community had begun to gather information suggesting it was the work of extremists either affiliated with or inspired by al Qaeda groups.
CNN's Carol Cratty and Barbara Starr contributed to this report