President Obama promised swift justice will be delivered to the people responsible for killing the United States ambassador to Libya and three other Americans during a Sept. 11 assault that Washington officials now believe was a coordinated attack rather than the actions of an angry, spontaneous mob.

Ambassador J. Christopher Stevens was killed, along with Foreign Service Officer Sean Smith and two U.S. Marines, after the American Embassy in Benghazi was set ablaze and fired upon by rocket-propelled grenades and other firearms.

The Associated Press reported Wednesday that a Libyan doctor is claiming he was unable to revive Stevens, who he said died of severe asphyxiation from smoke inhalation.

"Make no mistake: we will work with the Libyan government to bring to justice the killers who attacked our people," Obama said from the Rose Garden on Wednesday, with Secretary of State Hillary Clinton by his side.

The incident has moved foreign policy and national security to the center of the November presidential election.

Up until Wednesday, Obama and his opponent, Republican presidential nominee Mitt Romney, have been focused almost exclusively on economic issues.

But Romney swiftly criticized the Obama administration late Tuesday and again Wednesday in response to an apology issued by the American Embassy in Cairo for an anti-Muslim film produced in the United States that appeared to have sparked mob violence in both Egypt and Libya.

A statement published online by the embassy read: "The Embassy of the United States in Cairo condemns the continuing efforts by misguided individuals to hurt the religious feelings of Muslims - as we condemn efforts to offend believers of all religions."

Obama administration officials later said the statement was not authorized by the White House, and it was removed.

But Romney called it an indication that the Obama administration issues mixed signals on its foreign policy position.

"It's disgraceful that the Obama administration's first response was not to condemn attacks on our diplomatic missions, but to sympathize with those who waged the attacks," Romney said.

Romney then came under attack from Democrats for speaking out on the matter before Obama had a chance to address the nation.

Former Democratic presidential candidate John Kerry, a senator from Massachusetts who chairs the Senate Foreign Relations Committee, said Romney should apologize for speaking out.

The violence was apparently planned after a movie was posted online that dubbed Islam a "cancer" and depicted the Prophet Muhammad as a womanizing lunatic. A California real estate developer named Sam Bacile, who told the Associated Press he was an Israeli as well as an American citizen, produced the film and posted it online.

Sensing an opening in foreign policy, which has been a weakness for Romney, Republicans in both the House and Senate echoed the nominee's criticism of the administration.

House Armed Services Committee Chairman Buck McKeon, R-Calif., said Obama's apologetic stance with foreign nations has created the atmosphere that made Tuesday's attacks possible.

"Again and again under President Obama we have met threats and thugs with apologies and concessions," McKeon said in a statement. "Unsurprisingly, these mobs aren't satisfied with apologies anymore, they have clearly been escalating the offensive in the war of ideas for some time. Is it any wonder that events spun out of control and that American lives were lost?"