Obama vows to 'bring justice' to killers in US Embassy attack in Libya

President Obama condemned the "outrageous and shocking" attack on the U.S. Consulate in Benghazi that left the U.S. ambassador and three other Americans dead, as he and other officials vowed to "bring justice" to the killers while moving quickly to bolster security in Libya and at other diplomatic posts.

"Make no mistake. Justice will be done," Obama said, speaking from the Rose Garden alongside Secretary of State Hillary Clinton.

Those who knew Ambassador J. Christopher Stevens and the others killed expressed shock and grief Wednesday at the tragedy, which occurred on the 11th anniversary of the Sept. 11 attacks. Obama and Clinton both condemned the killers, while stressing that the U.S. bond with the Libyan government would not suffer as a result.

"Make no mistake. We will work with the Libyan government to bring justice to killers who attack our people," Obama said, adding:  "There is absolutely no justification to this type of senseless violence. None."

Stevens was killed Tuesday night when he and a group of embassy employees went to the consulate to try to evacuate staff. The protesters, purportedly angry over a film that ridiculed Islam's Prophet Muhammad, were firing gunshots and rocket-propelled grenades.

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Obama and Clinton offered new details Wednesday about the chaotic aftermath. They said some Libyans tried to fight to defend the U.S. post while it was under attack, even carrying Stevens' body to a hospital. The Libyan doctor who treated Stevens also told The Associated Press that he died of severe asphyxiation, apparently from smoke inhalation, and that he tried for 90 minutes to revive him.

Clinton, speaking from the State Department, called the tragedy "an attack that should shock the conscience of people of all faiths."

She vowed that those responsible would be "brought to justice." However, she said the U.S. would not turn away from Libya.

"Today, many Americans are asking, indeed I ask myself ... How could this happen in a country we helped liberate in a city we helped save from destruction?" Clinton said. "We must be clear-eyed even in our grief. ... This was an attack by a small and savage group, not the people or government of Libya."

Obama, in a statement Wednesday morning, said he's directed the administration to provide "all necessary resources" to support security for U.S. personnel in Libya and to increase security at diplomatic offices around the world. One U.S. official said a team of 50 Marines is being deployed to Benghazi to secure the compound.

Obama's presidential rival Mitt Romney also addressed the tragedy during a stop in Florida. Romney called the attack "disgusting," as he also criticized the Obama administration for an Egypt Embassy statement that initially expressed sympathy for those offended by the Islam film. That was in connection with a separate attack on the U.S. Embassy in Cairo.

Obama made clear in his written statement that the administration firmly condemns the violence.

"While the United States rejects efforts to denigrate the religious beliefs of others, we must all unequivocally oppose the kind of senseless violence that took the lives of these public servants," Obama said.

Obama called Stevens "a courageous and exemplary representative of the United States" who "selflessly served our country and the Libyan people" throughout the Libyan revolution.

"His legacy will endure wherever human beings reach for liberty and justice," the president said.

The State Department identified one of the other three Americans killed as Foreign Service Information Management Officer Sean Smith, a husband and father of two who had worked for the State Department for 10 years. The U.S. government is still notifying the next of kin for the other two individuals killed, and has not identified them.

Clinton described Stevens as a passionate and dedicated diplomat who had devoted himself to the transition in post-Qaddafi Libya.

"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," she said.

Stevens was appointed as ambassador to Libya in May 2012.

He served as a special representative to the Libyan Transitional National Council during the revolution in 2011, and as the deputy chief of mission from 2007 to 2009. Originally from California, Stevens was an international trade lawyer before joining the Foreign Service in the early 1990s. He also served as a volunteer in the Peace Corps from 1983 to 1985, teaching English in Morocco.

U.S. officials remain on alert for violence at other diplomatic posts.

Hours before the Benghazi attack, hundreds of mainly ultraconservative Islamist protesters in Egypt marched to the U.S. Embassy in downtown Cairo, gathering outside its walls and chanting against the movie and the U.S. Most of the embassy staff had left the compound earlier because of warnings of the upcoming demonstration.

Dozens of protesters then scaled the embassy walls, and several went into the courtyard and took down the American flag from a pole.

They brought it back to the crowd outside, which tried to burn it, but failing that tore it apart. The protesters on the wall then raised on the flagpole a black flag with a Muslim declaration of faith, "There is no god but God and Muhammad is his prophet." The flag, similar to the banner used by Al Qaeda, is commonly used by ultraconservatives around the region.

On Wednesday, the U.S. Embassy in Algiers was warning Americans in the country to avoid non-essential travel amid calls for more protests after the Libya attack.

The Associated Press contributed to this report.