The mall attack is the deadliest terror attack in Kenya since al Qaeda blew up the U.S. Embassy there in 1998, killing 213 people.
On Monday, Kenya's foreign minister told CNN it's clear that Al-Shabaab was not acting alone.
"This bares the hallmarks of al Qaeda. This is not just Al-Shabaab. In fact, the leaders are not Somali, as you may have heard. This was al Qaeda. It was a very well-coordinated effort, it was very well planned," Mohamed said.
But the attackers' national origins are irrelevant, she said.
"It doesn't matter where they come from. There are some Americans. There are some Brits. There are some others. It has nothing to do with the nationality of people," Mohamed said. "They are all evil and we must deal with them as such."
Lenku said that Monday's effort to roust the terrorists was a Kenyan operation, but government sources told CNN that Israeli special forces also were at the scene.
Kenyatta, the Kenyan president, vowed Sunday to punish those responsible for the attacks.
"They shall not get away with their despicable, beastly acts. Like the cowardly perpetrators now cornered in the building, we will punish the masterminds swiftly and indeed very painfully," he said.
U.S. Secretary of State John Kerry promised an American investigation.
"Obviously, it's an enormous offense against everybody's sense of right and wrong," Kerry said. "It represents the seriousness and the breadth of the challenge we face with ruthless and completely reckless terrorists, and we're going to pursue them."