U.S. Vows to Hunt Down Perpetrators of Benghazi Attack

President Barack Obama

Washington (CNN) -- The United States on Wednesday vowed to avenge the killings of its ambassador to Libya and three other Americans, moving warships toward the Libyan coast and preparing to track the suspected perpetrators with surveillance drones, officials said.

The slain ambassador, Chris Stevens, helped save Libya's eastern city of Benghazi during last year's revolution. He died there Tuesday night, along with another diplomat and two State Department security officers, when a mob stormed the U.S. Consulate and set it ablaze.

The Benghazi consulate was one of several American diplomatic missions that faced protests after the online release of a film that ridiculed Muslims and depicted the Prophet Mohammed as a child molester, womanizer and ruthless killer.

But U.S. sources said Wednesday the four-hour assault in Benghazi had been planned, with the attackers using the protest as a diversion.

"We will not waver in our commitment to see that justice is done for this terrible act," President Barack Obama said. "And make no mistake, justice will be done."