An FBI investigative team arrived at the site of last month's deadly attack on the U.S. Consulate in eastern Libya, Pentagon spokesman George Little said Thursday.
The military provided security, and both the FBI and military left Benghazi "a short time ago," he said.
Earlier, a senior administration official told CNN the team arrived late Wednesday and was working through Thursday, examining the outpost.
Officials said the military presence was an indication of ongoing security concerns in the region.
The September 11 consulate attack killed U.S. Ambassador to Libya J. Christopher Stevens and three other Americans.
The incident fueled increased global scrutiny of the North African nation led by a government that toppled dictator Moammar Gadhafi last year.
It also sparked political debate over whether the Obama administration has been forthcoming about its understanding of events.
The FBI visit to Benghazi had been stalled for more than three weeks because of security concerns at the site.
FBI and military officials have said they would need proper military protection in case of another attack on the U.S. Consulate.
The official described the support as both visible and more covert, suggesting the use of intelligence assets to monitor communications and the surrounding areas. The military team was "relatively small," the official said.
The visit happened after the Libyans approved the presence of the FBI and the U.S. military in Benghazi.
The U.S. military force providing security also was approved by Libyan government, the official said.
Kevin Perkins, FBI associate deputy director, said at a congressional hearing on September 19 that there are a "significant number of FBI agents, analysts and various support employees 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 said before 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 were left unsecured.
CNN discovered Stevens' journal during a visit by senior correspondent Arwa Damon to the unguarded abandoned compound three days after the attack.
This week, a Washington Post reporter visiting the site found sensitive documents, including personnel records of Libyans who were contracted to provide security, emergency evacuation protocols and details of U.S. weapons collection efforts.
But a State Department official told CNN the compound did not have any classified documents on the premises.
In the days after the assault on the Benghazi consulate, U.S. administration officials offered conflicting assessments on what led to the fatal security breach.
Some top officials said the violence erupted spontaneously amid a large protest about a U.S. made film that mocked the Prophet Mohammed.
But the U.S. intelligence community eventually revised its assessment, saying it now believes it was a deliberate terrorist assault.
The intelligence community now believes it was "a deliberate and organized terrorist assault carried out by extremists" affiliated or sympathetic with al Qaeda.
Defense Secretary Leon Panetta has said he believed the attack was "clearly" conducted by terrorists who planned it, and said 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 began to gather information suggesting it was the work of extremists either affiliated with al Qaeda groups or inspired by them.