FBI can't get to Benghazi, sources say

• CNN's Townsend: FBI agents are in Tripoli, waiting for approval to go to Benghazi
• "Bureaucratic infighting" has complicated the investigation, she says
• The crime scene in Benghazi has not been secured, Townsend says
• Source: "If we get there now, it's not clear it will be of any use to us"

(CNN) -- More than two weeks after four Americans -- including the U.S. ambassador to Libya -- were killed in an attack on the U.S. Consulate in Benghazi, FBI agents have not yet been granted access to investigate in the eastern Libyan city, and the crime scene has not been secured, sources said.

"They've gotten as far as Tripoli now, but they've never gotten to Benghazi," CNN National Security Analyst Fran Townsend said Wednesday, citing senior law enforcement officials.

Last Thursday, U.S. Secretary of State Hillary Clinton told reporters that an FBI team had reached Libya earlier in the week.

"In fairness to the secretary, it may be that she wanted to be coy about where they were in Libya for security concerns. That's understandable. But the fact is, it's not clear they've been in Libya for very long," Townsend said on CNN's "Anderson Cooper 360°."

"They had difficulty, and we understand there was some bureaucratic infighting between the FBI and Justice Department on the one hand, and the State Department on the other, and so it took them longer than they would have liked to get into country. They've now gotten there. But they still are unable to get permission to go to Benghazi."

FBI agents have made a request through the U.S. State Department for the crime scene to be secured, Townsend said, but that has not happened.

"The senior law enforcement official I spoke to said, 'If we get there now, it's not clear that it will be of any use to us,'" Townsend said.

The FBI team has conducted interviews of State Department and U.S. government personnel who were in Libya at the time of the attack, Townsend said, but the FBI's request to directly question individuals who Libyan authorities have in custody was denied.

U.S. Ambassador Chris Stevens was one of four Americans slain in the September 11 assault, when the U.S. Consulate in Benghazi came under attack amid a large protest about a U.S.-made film that mocked the Muslim Prophet Mohammed.

Speaking to reporters last Thursday, White House spokesman Jay Carney said the assault was a "terrorist attack."