Seven Americans made it out safely. The overall death toll from the standoff has surpassed 80.
The deceased Americans were identified as Victor Lynn Lovelady and Gordon Lee Rowan, the official said, speaking on condition of anonymity because he wasn't authorized to speak publicly about the matter. The official had no details on how the Americans died, and their hometowns were not released. The FBI has recovered the bodies of and notified the families.
Militants who attacked the Ain Amenas gas field in the Sahara had offered to release the pair in exchange for the freedom of two prominent terror suspects jailed in the United States: Omar Abdel Rahman, a blind sheik convicted of plotting to blow up New York City landmarks and considered the spiritual leader of the 1993 World Trade Center bombing, and Aafia Siddiqui, a Pakistani scientist convicted of shooting at two US soldiers in Afghanistan.
The Obama administration rejected the offer.
Last week's desert siege began Wednesday when Mali-based, Al-Qaeda-linked militants attempted to hijack two buses at the plant, were repelled, and then seized the gas refinery. They said the attack was retaliation for France's recent military intervention against Islamist rebels in neighboring Mali, but security experts argue it must have taken weeks of planning to hit the remote site.
One American death was confirmed Friday, that of Texas resident Frederick Buttaccio. Five Americans had been taken out of the country before Saturday's final assault by Algerian forces against the militants.
The US official said two further Americans survived the four-day crisis at an insecure oil rig at the facility. They were flown out to London on Saturday.
Algeria said after Saturday's assault by government forces that at least 32 extremists and 23 hostages of all nationalities were killed. On Sunday, the Algerian bomb squads found 25 more bodies, according to a security official, who spoke on condition of anonymity because of the sensitivity of the situation. And a wounded Romanian who had been evacuated later died.