The Libyan doctor who treated U.S. ambassador Chris Stevens says the diplomat died of severe asphyxiation and that he tried for 90 minutes to revive him.

Ziad Abu Zeid told The Associated Press on Wednesday that Stevens was brought to the Benghazi Medical Center by Libyans the night before, with no other Americans and that initially no one realized he was the ambassador.

Abu Zeid said Stevens had "severe asphyxia," apparently from smoke inhalation, causing stomach bleeding, but had no other injuries.

Stevens and three American security guards died when the U.S. Consulate in Benghazi came under attack from a mob angry over an anti-Islam film made in the U.S. The crowd fired guns and rocket-propelled grenades and set fire to the consulate.

THIS IS A BREAKING NEWS UPDATE. Check back soon for further information. AP's earlier story is below.

The U.S. ambassador to Libya and three other Americans were killed in an attack on the U.S. Consulate in Benghazi by protesters angry over a film that ridiculed Islam's Prophet Muhammad.

Ambassador Chris Stevens, 52, died as he and a group of embassy employees went to the consulate to try to evacuate staff as the building came under attack by a mob firing machine-guns and rocket-propelled grenades. He was the first U.S. ambassador to be killed in the line of duty since 1979.

President Barack Obama ordered increased security to protect American diplomatic personnel around world.

"I strongly condemn the outrageous attack on our diplomatic facility in Benghazi," Obama said, adding the four Americans "exemplified America's commitment to freedom, justice, and partnership with nations and people around the globe."

Libya's interim president, Mohammed el-Megarif, apologized to the United States for the attack, which he described as "cowardly." Speaking to reporters, he offered his condolences on the death of the four Americans and vowed to bring the culprits to justice and maintain his country's close relations with the United States.

The three Americans killed with Stevens were security guards, he said.

"We extend our apology to America, the American people and the whole world," el-Megarif said.

The attack in Libya came hours after Egyptian protesters climbed the walls of the U.S. Embassy in Cairo, pulling down the American flag and temporarily replacing it with a black Islamic banner.

The brazen assaults _ the first on U.S. diplomatic facilities in either country _ underscored the lawlessness that has taken hold in both Egypt and Libya after revolutions ousted their autocratic secular regimes and upended the tightly controlled police state in both countries. Islamists, who were long repressed under the previous regimes, have emerged as a powerful force but new governments in both nations are struggling to achieve stability.

Egypt's police, a onetime hated force blamed for massive human rights abuses, have yet to fully take back the streets after Hosni Mubarak's ouster in February 2011.

On Tuesday, riot police stood by the embassy's walls but continued to allow protesters to climb them for several hours. The protesters, however, appeared to intentionally stick to certain limits: A few entered the embassy grounds to remove the flags and come back, but otherwise the chanting youth stayed on top of the walls without storming the compound or damaging property.

The uproar over the film also poses a new test for Egypt's new Islamist president, Mohammed Morsi, who has yet to condemn the riot outside the U.S. Embassy in Cairo or say anything about the offending film. The protest was by mostly ultraconservative Islamists.

The film was produced by a California filmmaker who identifies himself as both American and Israeli, though Israeli officials said Wednesday they had no record of him as a citizen. The film was being promoted by an extreme anti-Muslim Egyptian Christian campaigner in the United States. Excerpts from the film dubbed into Arabic were posted on YouTube. The video depicts Muhammad as a fraud, a womanizer and a madman in an overtly ridiculing way, showing him having sex and calling for massacres.

Ultraconservative Islamists also were suspected of being behind the Benghazi attack. Advocating a strict interpretation of Islam, they have bulldozed Sufi shrines and mosques that house tombs in the Libyan capital, Tripoli, and other cities, including ancient sites dating back to 5,000 years ago.

Heavily armed, ultraconservative groups like Ansar al-Shariah, or Supporters of Shariah, have claimed responsibility for the attacks on the shrines, declaring Sufi practices as "heretical."

Libya has been also hit by a series of recent attacks that served as evidence of the deep and persistent security vacuum in the country after the fall of Moammar Gadhafi's regime, which was ousted by rebels backed by a NATO air campaign. Many Libyans believe that unrest in their country is in part the work of Gadhafi's loyalists who want to undermine efforts to rebuild the country after last year's ruinous civil war.

Stevens was a career diplomat who spoke Arabic and French and had already served two tours in Libya, including running the office in Benghazi during the revolt against Gadhafi. He was confirmed as ambassador to Libya by the Senate earlier this year.

Before Tuesday, five U.S. ambassadors had been killed in the line of duty, the last being Adolph Dubs in Afghanistan in 1979, according to the State Department historian's office.

The protests were sparked by an obscure, two-hour movie titled "Innocence of Muslims," which came to attention in Egypt after its trailer was dubbed into Arabic and posted on YouTube.

Sam Bacile, a 56-year-old California real estate developer, said he wrote, produced and directed the movie.

Bacile told The Associated Press he was an Israeli Jew and an American citizen.

Israeli officials said Wednesday they had not heard of Bacile and there was no record of him being a citizen. They spoke on condition of anonymity because they are not permitted to share personal information with the media.

Bacile said he had not anticipated such a furious reaction. Speaking by phone from an undisclosed location, Bacile, who went into hiding Tuesday, remained defiant, saying Islam is a cancer and that he intended his film to be a provocative political statement condemning the religion.

Bacile said he believes the movie will help his native land by exposing Islam's flaws to the world. "Islam is a cancer, period," he repeatedly said in a solemn, accented tone.

Israel, however, sought to distance itself from Bacile.

"It's obvious we'll have to be vigilant. Anything he did or said has nothing to do whatsoever with Israel. He may claim what he wants. This was not done with or for or through Israel." Foreign Ministry spokesman Yigal Palmor said on Wednesday.

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Michael reported from Cairo. Associated Press writers Matthew Lee in Washington and Joseph Federman in Jerusalem contributed to this report.