Gen Julius Karangi, chief of Kenya's military, identified the sacked soldiers as Victor Otieno and Victor Ashiundu and said they were in detention pending formal charges.
He said the two soldiers were found with mobile phones, cameras and chargers that were stolen from the mall during the siege.
"Discipline is our core driving point and we are not playing with this issue," he said. "That is why we have taken action on these soldiers. Two of them have been jailed and dismissed while a third one is under probe."
In a separate development, police said they were set to charge five suspects over their alleged roles in the attack in which 67 people were killed.
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The attack was the largest in Kenya since the 1998 bombings by al-Qaida of the United States Embassy in Nairobi. The Somali Islamic extremist group al-Shabab claimed responsibly for the mall attack, saying it was in retribution for Kenya's military involvement in Somalia.
Local and foreign investigators have since been digging through the rubble for evidence, and at least four bodies believed to be those mall's attackers have been retrieved.
Ndegwa Muhoro, Kenya's director of criminal investigations, said today that five suspects were in custody and that two other suspects believed to have played a role in the attack are still at large. He identified the wanted suspects as Kenyan national Abdikadir Haret Mohamed, who also is known as Mohamed Hussein, as well as a Somali national named Adan Dheq. Dheq also is known as Hussein Abdi Ali or Abdulahi Dugon Subow. The two suspects owned the Mitsubishu salon car registration that police seized outside the mall nearly a week after the attack. Police found explosives and weapons inside the car, he said.