Abbas Gullet said there are likely more dead from the attack that saw gunmen using grenades and gunfire.
Kenya's military surrounded the Westgate mall hours after the midday attack in the upscale Westlands neighbourhood in Kenya's capital.
Nairobi police Chief Benson Kibue blamed the attack on terrorists, though he did not name a group.
A witness said that the attackers said they were targeting non-Muslims.
An al-Qaeda-linked Somali militant group had threatened large-scale attacks on Kenya for sending its military into Somalia.
