* Mueller meets Libyan prime minister, other officials
* US investigators still seeking leads in Benghazi attack
* Republican criticizes 'lack of results'
WASHINGTON/TRIPOLI, Jan 17 (Reuters) - FBI Director Robert Mueller visited Libya on Thursday, an FBI official said, as U.S. investigators continued their inquiry into the September attack in Benghazi in which U.S. Ambassador to Libya Christopher Stevens and three other Americans were killed.
"The director's visit was an opportunity to discuss ongoing cooperation on a number of issues," said the FBI official, who spoke on condition of anonymity.
Mueller met with several senior Libyan officials, including Prime Minister Ali Zeidan, the justice minister and the intelligence chief, a Libyan government source said, adding that the meetings were secret.
FBI agents went to Benghazi in October to analyze the crime scene but have since remained in Tripoli because of security concerns. In an effort to generate leads, the FBI has put out a poster asking for information.
U.S. officials have not announced the capture of any suspects in the attack, although President Barack Obama said in December that investigators have some "very good leads."
Obama, in a speech the day after the attack, said he would "work with the Libyan government to bring to justice the killers who attacked our people."
The security of the U.S. diplomatic sites in Benghazi has become a political flashpoint for the Obama administration. A Senate report in December said the State Department did not focus tightly enough on Libyan extremists or react quickly enough to threat assessments in the weeks before the attack.
The pace of the investigation has become yet another source of criticism.
"The way it's been handled and the lack of results have only served to embolden our enemies as demonstrated by the events in Algeria this week. They have not seen a consequence for their actions," said Republican Representative Michael McCaul in a statement. McCaul is chairman of the U.S. House Homeland Security Committee.
Islamist militants in Algeria stormed a natural gas facility on Wednesday and said they were holding 41 foreigners in response to a French military operation in neighboring Mali.
A U.S. Justice Department spokesman declined to comment on Thursday on the pace of the Benghazi investigation.
Secretary of State Hillary Clinton is scheduled to discuss the attack with two congressional committees on Jan. 23.