Dark smoke that rose from the building after Monday's assault was from fires set by the gunmen to distract forces from the assault, Lenku said.
Terrorists appear to be on the run inside the mall, which Lenku said had been sealed off to prevent their escape.
"We are in charge of the situation, our people are safe," he said.
Before the assault, terrorists from the Somalia-based Al-Shabaab group were believed to have about 10 hostages on one level of the mall, security officials said.