U.S. officials are investigating whether the attack in Benghazi that killed the American ambassador to Libya and three other diplomats was planned, as two warships sent by the Pentagon sailed towards the North African nation's coast.

U.S. President Barack Obama condemned the deadly assault on the U.S. consulate in the eastern Libyan city, saying that "no acts of terror" would shake America's resolve.

Chris Stevens, the U.S. ambassador to Libya, was among the four Americans slain in Tuesday's fiery assault. The other victims were consulate staffers.

"Make no mistake — justice will be done," Obama said Wednesday in a brief statement outside the White House, alongside Secretary of State Hillary Rodham Clinton. "We reject all efforts to denigrate the religious beliefs of others. But there is absolutely no justification for this type of senseless violence. None."

In remarks about Stevens, Obama characterized the ambassador as a model diplomat who was passionate about seeing a new, democratic Libya.

"It's especially tragic that Chris Stevens died in Benghazi because it is a city that he helped to save at the height of the Libyan revolution," the president said.

Hours after his remarks, U.S. officials told The Associated Press that the Pentagon had dispatched two destroyers — both of which carry Tomahawk missiles — to move towards Libya. The USS Laboon was stationed off the coast on Wednesday while the USS McFaul was due to arrive within days.

The warships don't have a specific mission, officials said, although they were standing by to respond to orders from the president. The officials spoke on condition of anonymity because they were not authorized to publicly discuss troop movements.

In the meantime, Obama has instructed U.S. diplomatic missions around the world to boost their security.

The consulate attack was reportedly carried out by Libyans outraged by an amateur U.S. film that ridicules the Prophet Muhammad. However, U.S. investigators are reportedly probing whether an armed extremist group may have been to blame.

Henry Crumpton, a former deputy director for the CIA's Counter-Terrorism Center, told the CBC's Evan Solomon on Power & Politics that the attacks in Benghazi appear to bear the hallmarks of an organized militant network such as al-Qaeda.

"I don't know who was behind the attack, but it certainly has … the signature of an attack that required some planning, some preparation, and it was obviously executed with a deadly and horrible precision," he said.

Crumpton said that the circumstances behind the violence — including the target and the significance of the date of the attacks — would raise suspicions in intelligence circles. The violence erupted 11 years after the Sept. 11, 2001, co-ordinated attacks on the U.S.

'As the conflict in Libya unfolded, Chris was one of the first Americans on the ground in Benghazi. He risked his own life to lend the Libyan people a helping hand to build the foundation for a new, free nation.'—U.S. Secretary of State Hillary Clinton

Attacking a "hard target" such as an official U.S. installation in a foreign country would require careful planning, he said.

"Particularly for a country like Libya, where there has been recent hostilities, and on a day — the anniversary of 9/11 — clearly I think that this required some type of surveillance, some type of planning, preparation and then the execution," he said.

Crumpton said it can't be ruled out that the inflammatory anti-Islam film was being used as a convenient "excuse" or "perverted justification" for the attack.

An American counterterrorism official also told The Associated Press that the events that transpired Tuesday night at the Benghazi consulate were "too co-ordinated or professional to be spontaneous."

The official spoke on condition of anonymity because he was not authorized to discuss the incident publicly.

Attack may have been planned

The White House also believes that Stevens may have been killed in a premeditated attack, rather than a spontaneous protest that turned violent, the New York Times reported.

The newspaper cited unnamed American officials saying they have been comparing a protest in Cairo on Tuesday with the event that took place in Benghazi, where participants appeared to be armed.

Libya's deputy UN ambassador, Ibrahim Dabbashi, blamed "an extremist group" for the diplomats' deaths, which he said "in no way serves the interests of the people or the Libyan authorities, and cannot be considered a defence of Islam."

The U.S. plans to use unmanned surveillance drones to search for militant camps and other targets in eastern Libya that could be linked to the consulate attack, CNN reported.

The State Department identified one of the other slain Americans as information management officer Sean Smith, a married father of two and a 10-year veteran of the U.S. Foreign Service.

The Associated Press, citing anonymous sources, said 50 marines will be sent to Libya to beef up security at the diplomatic posts in the country.

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U.S. envoy Chris Stevens speaks to local media at the Tibesty Hotel in Benghazi, Libya, on April 11, 2011. (Ben Curtis/Associated Press)

There were conflicting reports of the circumstances surrounding the deaths Tuesday night. Al-Jazeera reported Stevens died of smoke inhalation after a mob attacked the consulate and set it on fire. Reuters, citing an unnamed Libyan official, said the four Americans died after militants fired rockets at their car in Benghazi.

Stevens and three other employees of the U.S. Embassy in Libya went to the consulate in Benghazi in an attempt to get staff to safety after the building came under attack, The Associated Press reported.

'Friend of Libya' killed

Clinton said Wednesday the attack was carried out by a "small but savage" group, noting that other Libyans carried Stevens's body to the hospital and helped other Americans to safety.She said the U.S.-Libyan friendship will not be a casualty of the violence.

Meanwhile Libya's deputy prime minister, Mustafa Bushagar, condemned on Twitter what he called "the cowardly act of attacking the U.S. consulate and the killing of Mr. Stevens and the other diplomats." 

"Ambassador Stevens was a friend of Libya and we are shocked at the attacks on the US consulate in Benghazi," Bushagar said. "I condemn these barbaric acts in the strongest possible terms. This is an attack on America, Libya and free people everywhere."

Canadian Foreign Affairs Minister John Baird described the attack as "senseless" and called on Libyan authorities "to take all necessary measures to protect diplomatic premises in accordance with Libya's international obligations."

"We also urge Libyan officials to ensure the extremists responsible are brought to swift justice," Baird said in a statement.

Israeli Prime Minister Benjamin Netanyahu also sent his condolences to the families of the American victims, calling the death of Stevens a "tragic murder."

Filmmaker in hiding

A man who identified himself to The Associated Press as an "Israeli Jew" and California filmmaker named Sam Bacile is at the centre of the outrage that may have prompted the attacks, after a trailer featuring scenes from a two-hour movie, titled Innocence of Muslims, was posted online.

The YouTube video depicts the Prophet Muhammad as a fraud, womanizer and madman in an overtly ridiculing way, showing him having sex and calling for massacres.

A 14-minute film trailer was posted on YouTube in English, and a second version dubbed into Egyptian Arabic was added later. YouTube said it would not remove the video from its website. But it has blocked the video in Egypt, where anger over the film touched off protests Tuesday that saw crowds scale the walls of the U.S. Embassy in Cairo, pull down the American flag and replace it with an Islamic banner.

The attacks were said to be the first on American diplomatic posts in either Libya or Egypt.

In Tunisia, Reuters reported Wednesday that police fired tear gas and rubber bullets at protesters near the U.S. Embassy. About 50 people were said to have burned and trampled American flags in protest over the film. 

Reuters reported the government of Afghanistan had banned the YouTube site to prevent Afghans from seeing the video that led to the violence in Libya and Egypt.

Praised by Clinton

Stevens, 52, has become the fifth U.S. ambassador killed while on duty, and the first since Adolph Dubs was killed in Afghanistan in 1979.

A career diplomat, Stevens took over as U.S. ambassador to Libya in May. He had previously served two diplomatic postings in Libya, including a stint in Benghazi during the revolt that brought down former ruler Moammar Gadhafi.

Clinton said Stevens "fell in love" with the Middle East while teaching English in Morocco.

"I had the privilege of swearing in Chris for his post in Libya only a few months ago," Clinton said.

"He spoke eloquently about his passion for service, for diplomacy and for the Libyan people. …As the conflict in Libya unfolded, Chris was one of the first Americans on the ground in Benghazi. He risked his own life to lend the Libyan people a helping hand to build the foundation for a new, free nation."

Corrections

  • This story has been altered to remove details provided by The Associated Press about the identity of the filmmaker behind Innocence of Muslims: The Associated Press quoted a man who identified himself in several phone conversations as Sam Bacile, and who said he wrote and directed the film. The AP story quoted him saying he was an Israeli Jew. In later reporting, the AP was unable to find any public records confirming the existence of a person with that name. The AP subsequently reported that Nakoula Basseley Nakoula was the key figure behind the film. Federal authorities confirmed that finding. A federal law enforcement official told The Associated Press on Thursday that authorities had connected Nakoula to the man using the pseudonym of Sam Bacile. Federal court papers filed against Nakoula in a 2010 criminal prosecution noted that Nakoula had used numerous aliases, including Nicola Bacily and Robert Bacily. Nakoula told the AP on Wednesday that he is a Coptic Christian. The person claiming to be Bacile said in his conversation with the AP that the film was financed with the help of more than 100 Jewish donors. According to Film L.A. Inc., which grants filming permits in Los Angeles County, the production company for the film was a Duarte, Calif.-based Christian group, Media for Christ. The president of that organization is a Christian from Egypt.
    Sep 13, 2013 3:45 AM ET
With files from The Associated Press