Al-Libi was the No. 2 man of the so-called core al Qaeda along the Afghan and Pakistan border. A CIA drone strike in Pakistan killed him in June.

Al Qaeda in the Arabian Peninsula -- which did not claim involvement in the Libya attack -- is known as a substantial threat both in Yemen and beyond its borders.

The United States deployed warships and surveillance drones in its hunt for the killers of the diplomatic staffers, and a contingent of 50 Marines has arrived to boost the security of Americans in the country.

The United States and Libya have embarked on a new relationship since rebels toppled longtime dictator Moammar Gadhafi last year.

U.S. warplanes participated in the NATO effort that helped the Benghazi-based rebellion against Gadhafi, who was wanted by the International Criminal Court for charges of crimes against humanity before he was killed in October.