TRIPOLI (Reuters) - Libya and the United States have yet to agree how a U.S. investigative team will cooperate in a probe into a deadly attack on the U.S. diplomatic mission in Benghazi, a senior Libyan official said on Tuesday.

FBI agents were sent to Libya after the September 11 attack on the U.S. diplomatic mission and another facility in which the U.S. ambassador and three other Americans died. So far they have conducted interviews in Tripoli and have yet to go to Benghazi.

Deputy Foreign Minister Mohammed Abdel Aziz said the prosecutor general had given only verbal approval for a joint investigation.

"We are getting ready for the FBI team to go to Benghazi and meet with our team and start joint investigations together and also visit the site," he said.

"The FBI team is now in Tripoli. There are others who will come maybe soon to join the team ... Hopefully in the coming days we will reach an agreement as to how the (U.S.) team will work with the Libyan team ... We are now in the context of (awaiting) written permission."

Abdel Aziz was speaking after meeting U.S. Assistant Secretary of State for Near Eastern Affairs Elizabeth Jones in Tripoli. "It is the right of the United States to be involved, exchange information and investigate what happened in Benghazi," Abdel Aziz said.

State Department spokeswoman Victoria Nuland sidestepped the question of whether an agreement had been reached with Libya, but said: "We have a commitment from the Libyan government to work together. There has been cooperation at the political level. There has to now be cooperation at the investigative level."

She said in State Department contacts with the FBI on Tuesday, "they expressed confidence that they'll be able to work well with the Libyans."

An FBI spokesman in Washington would only say that the investigation into the Benghazi attack was continuing, but would not comment on where the agents in Libya were located.

A U.S. lawmaker said security was a factor as to why the FBI team had yet not gone to Benghazi.

"Part of it was security posture, who was going to perform the security was part of it," House intelligence committee Chairman Mike Rogers told Reuters. "What worries me is that crime scene is so stale now and been well-trampled."

The head of Libya's Supreme Court, Kamal Dahan, who also met Jones on Tuesday, told reporters the two countries would cooperate but that Libya would lead the probe. Jones also met Prime Minister-elect Mustafa Abushagur.

The Obama administration has described the assault as a terrorist attack and announced a panel to investigate the events. Its work is separate from the FBI probe.

Libyan officials say eight people have been arrested so far in connection with the attack.

(Reporting by Ali Shuaib; Additional reporting by Arshad Mohammed and Tabassum Zakaria in Washington; Editing by Robin Pomeroy and Stacey Joyce)