U.S. Marines were dispatched to Libya to bolster security in the wake of the attack, The Washington Post reported. The Pentagon also directed two destroyers, the USS Laboon and USS McFaul, toward the Libyan coast, CNN reported. A senior official said the warships, equipped with satellite-guided Tomahawk cruise missiles that can be programmed to hit specific targets, "will give the administration flexibility," CNN said. The McFaul was at Crete in the Mediterranean and the Laboon was near Gibraltar.
Ambassador Christopher Stevens, Foreign Service Officer Sean Smith and two other Americans were killed when militants attacked the consulate Tuesday, angered over a 13-minute U.S.-made film clip depicting the Prophet Muhammad as a fake and womanizer.
"The United States condemns in the strongest terms this outrageous attack," Obama said Wednesday in a statement. "We will work with the Libyan government to bring justice to the killers who attacked our people."
Obama said the United States and Libya were working together to secure the safety of the U.S. diplomatic staff.
Twice during his statement, Obama said, "Justice will be done."
Interim Libyan President Mohamed Magariaf apologized to the United States for the attack, the Los Angeles Times reported. CNN said Prime Minister Abdurrahim el-Keib labeled it a "cowardly, criminal act."
Secretary of State Hillary Clinton was by Obama's side as he spoke, but did not speak. When Obama finished his statement, he and Clinton walked back into the White House, not addressing questions shouted from reporters.
The Defense Department ordered two Marine anti-terrorism security teams to Libya, a senior Marine official told the Post.
The FBI said in a statement it is investigating the attack as well, the Post said.
"The FBI will not speculate on the facts and circumstances surrounding the attacks," the FBI said in a statement.
The Imprisoned Omar Abdul Rahman Brigades, an al-Qaida-affiliated group that previously attacked the consulate, is the primary suspect in Tuesday's attack, sources tracking militant Islamist groups in eastern Libya told CNN. The sources said the attack came after al-Qaida leader Ayman al-Zawahiri said the June death of a senior Libyan member of the terror group Abu Yahya al-Libi must be avenged.
Rep. Mike Rogers, R-Mich., chairman of the House Intelligence Committee, said there was strong evidence the assault was premeditated.
"This was a well-armed, well-coordinated event," Rogers said in an interview on MSNBC. "It had both indirect and direct fire, and it had military maneuvers that were all part of this very organized attack."
Clinton said in an earlier statement the attack "should shock the conscience of people of all faiths around the world." Americans, including herself, were asking how such an attack could occur, she said.
"How could this happen in a country we helped liberate in a city we helped save from destruction? This question reflects just how complicated and at times how confounding the world can be," she said. "But 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."
"There is no justification for this violence," Obama said while noting the United States, since its founding, has rejected "all efforts to denigrate religious beliefs of others."
A senior U.S. official said two separate events were going on at the diplomatic compound -- a grenade attack outside and a fire created by a grenade inside the compound, CNN said.
Stevens and the others who died had gone to the roof of the consulate and had become separated from the others trying to leave the building. Stevens was overcome by smoke, the official told CNN.
CNN cited sources who said militants had planned an attack on the U.S. diplomatic facility and used the protests as cover to attack the consulate. CNN said the source said the attack did not necessarily target Stevens specifically.
USA Today reported Eric Trager of the Washington Institute for Near East Policy said the protest was planned by Salafists before word got out about the Muhammad film.
Obama said Libyan security forces fought the attackers, helped other staffers find safety and helped take Stevens to the hospital, where he was pronounced dead.
He said security was being ramped up for other U.S. embassies as well.
Obama called Stevens "a role model for all who worked with him" who, along with his colleagues, "died in a country trying to emerge from the [recent] experience of war. I have no doubt their legacy will live on."
Obama noted the attacks at the facilities in Cairo, where there were no injuries, and Benghazi occurred on the 11th anniversary of the Sept. 11, 2001, terrorist attacks on the United States, "already a painful day for our nation."
"As Americans, let us never ever forget that our freedom is sustained only because there are people willing to fight for it, stand up for it and lay down their lives for it.
"We will not waver to see that justice is done for this terrible act," Obama said. "And make no mistake, justice will be done."
Libyan Deputy Interior Ministry official Wanis al-Sharef said gunmen from the Ansar al-Sharia Islamist group fired rocket-propelled grenades at the consulate.
The violence in Benghazi followed protests in Egypt, where protesters in an angry crowd of about 2,000 people scaled the U.S. Embassy wall in Cairo Tuesday evening. Six police officers and a number of protesters were injured in a second day of rioting Wednesday, CNN reported.
They pulled down a U.S. flag and burned it, replacing the flag with a black banner with white letters reading, "There is no god but God and Muhammad is His Messenger," a phrase favored by ultraconservative Muslims and militants.
The mobs were set off by Egyptian media reports about the trailer -- accessible on YouTube -- for the video "Innocence of Muslims," made by Sam Bacile, a 52-year-old Israeli-American who has called Islam a "cancer."
Bacile told The Wall Street Journal he raised $5 million from 100 Jewish donors to produce the film, which shows the Prophet Muhammad as a homosexual son of undetermined patrimony who advocates child slavery and extramarital sex, for himself, in the name of religion.
The video was allegedly supported by conservative Egyptian Coptic Christians living in the United States, al-Jazeera said.
The Rev. Terry Jones of Gainesville, Fla., who inspired deadly riots in Afghanistan in 2010 and 2011 by threatening to burn copies of the Koran and then burning one in his church, said he would show the trailer at his church Tuesday night.
Mohammed Shafiq, chief executive director of the Ramadhan Foundation in Britain, condemned the violence as well as the "disgusting" film by Bacile.
"The only intention of this evil man is to cause harm to the hearts of Muslims and create more friction amongst our diverse communities," Shafiq said in a statement Wednesday. "Islam is ready to be challenged and questioned but to do it in such a way suggests their real intentions are to promote division and harm Muslims."
He called on the Jewish community to condemn the film and its financial backers. The Ramadhan Foundation, based in Manchester, England, said it forwarded its complaints to Obama and Clinton Wednesday.
"I also wish to condemn the killing of the U.S. ambassador in Benghazi yesterday [Tuesday] and the violence in Egypt," Shafiq said. "While we Muslims are hurting and disgusted at his [Bacile's] film, we must maintain peaceful protest and ensure we channel our anger towards those that have done such actions."
Flags flew at half-staff in Washington Wednesday.