The official, who insisted on anonymity because he is not authorized to give the information, told The Associated Press that the two are Ahmed Hassan Abubakar and Yahye Ahmed Osman. No details on the men were made available.
Authorities previously revealed the names of two other attackers as Abu Barat Al-Sudani, also known as Mohamed Hassan Dhuhulow, and Mohamed Abdinur Said. Dhuhulow had lived in Norway.
All four attackers were believed to be ethnic Somalis. Dennis Brady, the FBI legal attache in Nairobi, said last month that the FBI, like Kenyan authorities, believes all four attackers died inside the mall.
"Our ERT (Evidence Response Team) made significant finds, and there is no evidence that any of the attackers escaped from the area where they made their last stand," Brady said, adding that a secure crime scene perimeter made an escape unlikely.
Despite press reports during the mall siege that the attackers had hostages and had prepositioned weapons or ammunition inside the mall, no evidence has emerged to back those claims.
Four ethnic Somali men have been charged in Kenyan court with assisting the attackers. Their trials are ongoing.