President Barack Obama's counterterrorism chief has discussed last month's killing of the U.S. ambassador to Libya with the country's leaders.

John Brennan is in Tripoli as part of the investigation into the attack on the U.S. consulate in Benghazi last month, where Ambassador Chris Stevens was killed along with three other Americans. Brennan met Wednesday with interim President Mohammed el-Megarif and Foreign Minister Ashour bin Khayal.

Omar Humidan, spokesman for Libya's General National Council, said all agreed the investigation should be secret.

The U.S. has blamed militants linked to al-Qaida for the consulate attack. It erupted as Muslims protested a film that insulted Islam's Prophet Muhammad. The U.S. declared later that militants linked to the international terror network were involved.

Obama's Republican opponents have criticized his handling of the affair.