TRIPOLI, Libya » 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.