Plans had called for agents to arrive in the region Saturday, but officials said instability in Libya and elsewhere caused a delay in their arrival, CNN reported.
Citing a source, CNN said the FBI has determined there would be no advantage in sending people into a dangerous zone, and it was not clear when conditions might offer enough stability to send teams in.
For now, agents have been conducting interviews with witnesses outside Libya, including people who were evacuated following Tuesday's attack on the consulate, in which Ambassador Christopher Stevens and three other Americans were killed.
Libyan officials say they believe the attack was planned, and Libyan President Mohamed Magariaf told NBC News Saturday "foreigners" joined Libyans in carrying out the attack.
In an interview, Magariaf declined to say where the outsiders came from, but he said he was sharing the information with U.S. officials.
"We have assumptions and we have some information, and all that information we have now leads to the same direction about the perpetrators, the criminals," he said.