Updated 6:15 a.m. ET Sept. 13
(CBS/AP) WASHINGTON - The Obama administration, roiled by the first killing of a U.S. ambassador in more than 30 years, has begun what appears to be a terrorist hunt in Libya, as evidence mounts that the deaths of four diplomatic workers there were perpetrated by well-armed thugs and not an out-of-control crowd.
CBS News correspondent David Martin reports the FBI has opened an investigation into the deaths, and agents will be sent to sift through the wreckage for evidence. They will be accompanied by a second team sent just for their protection.
As part of the hunt for the attackers, officials say the U.S. will increase its surveillance over Libya, including the use of unmanned drones. In addition, the U.S. Navy is positioning two destroyers armed with cruise missiles off the coast of Libya.
One destroyer, the USS Laboon, moved to a position off the coast Wednesday, and the USS McFaul is en route and should be stationed off the coast within days. Officials said the ships, which carry Tomahawk cruise missiles, do not have a specific mission. But they give commanders flexibility to respond to any mission ordered by the president.
The investigation will focus on whether the assault on the U.S. Consulate in Libya was a planned terrorist strike to mark the anniversary of the Sept. 11, 2001, attacks and not a spontaneous mob enraged over an anti-Islam YouTube video.
After the attack, an elite anti-terrorist unit of about 40 Marines was flown in to beef up security at the American embassy in the capital of Tripoli. Air Force transport planes flew the bodies of the dead Americans out, along with at least three who were injured and the rest of the approximately 25 diplomats assigned to the consulate. At the same time, the U.S. State Department urged all non-essential personnel to leave on commercial flights.
Three Americans injured in the assault on the consulate in Benghazi were being treated Thursday at the U.S. military hospital in Landstuhl, Germany, near America's Ramstein Air Base, CBS News has learned.
Wanis al-Sharef, a Libyan Interior Ministry official in Benghazi, said there had been threats that Islamic militants might try to take revenge for the death of al Qaeda's No. 2 commander Abu Yahya al-Libi, who wasin June, and he said the U.S. consulate should have been better protected.
Confirming al-Libi's death for the first time in a video posted online Monday, al Qaeda chief Ayman Al-Zawahri called on Muslims in al-Libi's native Libya to take revenge for his death.
U.S. officials believe the militants were using the demonstration against the video as a cover to get into the consulate and then take as much revenge as they could on Americans, Martin reports.
While the White House has been hesitant to call the attack planned, House Intelligence Committee Chairman Mike Rogers was not so ambiguous.
"Absolutely it's a terrorist attack," Rogers told CBS News Capitol Hill producer Jill Jackson. "This was not done by the Libyan government. It was done by an external group we believe has at least extremist ties, maybe al Qaeda ties, and the style and the signature of the attack clearly would be something that we have seen before and would be in line with something al Qaeda would do."
The White House says President Obama called the presidents of Libya and Egypt Tuesday and urged them to continue working with the United States to ensure the safety of diplomatic personnel.
Mr. Obama thanked Libyan President Mohamed Magariaf for his condolences over the deaths of U.S. Ambassador J. Christopher Stevens and three other State Department officers during the assault on the U.S. consulate in Benghazi Tuesday. The White House says the two leaders agreed to work together to bring the attackers to justice.
During a second call, Egyptian President Mohammed Morsi promised Egypt "would honor its obligation to ensure the safety of American personnel," the White House said.
Mr. Obama told Morsi that while "he rejects efforts to denigrate Islam ... there is never any justification for violence against innocents."
In a White House appearance Tuesday, Mr. Obama said the U.S. would "work with the Libyan government to bring to justice" those who Stevens and three other Americans.
White House press secretary Jay Carney said it was too early to judge whether the attack was planned.
"I know that this is being investigated, and we're working with the Libyan government to investigate the incident. I would not want to speculate on that at this time," he said. Several Libyan security guards also were killed.
Rogers, R-Mich., said U.S. intelligence had not yet determined who was responsible, but added, "Our list is narrowing."
"When you see (such an attack), it wasn't some folks who had some guns in their garage and said let's shoot up the consulate," Rogers said.
Analysts are working on several different scenarios based on intelligence that could lead to a motive for the attack. Some concern the possibility of targeting high-ranking officials, according to a law enforcement official briefed on the investigation. But none of the intelligence thus far has suggested terrorists would specifically target Stevens, said the official who also spoke on condition of anonymity because he was not authorized to speak publicly about the investigation.
The attack in Libya, which came hours after a mob stormed the U.S. Embassy in Cairo and tore down the U.S. flag, was presumed to have been triggered by a movie, whose trailer has gone viral on YouTube, depicting the Islamic prophet Muhammad in disrespectful ways. In an extraordinary move, Gen. Martin Dempsey, the chairman of the Joint Chiefs of Staff, called anti-Islamic preacher Terry Jones and asked him to stop promoting the film. A spokeswoman said the church would not show the film Wednesday evening.
"Make no mistake. Justice will be done," a somber Obama pledged at the White House, Secretary of State Hillary Rodham Clinton at his side.
He ordered increased security at U.S. diplomatic missions overseas, particularly in Libya, and said he condemned "in the strongest possible terms the outrageous and shocking" attack. Clinton said she was particularly appalled that the attack took place in Benghazi, which the U.S. had helped liberate from dictator Muammar Qaddafi during the Arab Spring revolution in Libya last year.
Three Americans were wounded, U.S. officials said.
The aftermath of the two attacks also stirred the U.S. presidential campaign, where until Wednesday, foreign policy had taken a back seat to the struggling economy.
The Republican nominee, Mitt Romney, criticized the administration for statements issued before and after the Cairo attacks that expressed sympathy for those insulted by the video. But he in turn was criticized for turning a tragedy too quickly into political fodder, and getting key details wrong.