The threat drew a sharp response from Nadif Jama, the governor for Garissa county.

"The fallacy and satanic mindset of Al Shabaab is that in Somalia, they kill Muslims and Somalis," Jama said. "They cross the border here and then say they are killing non-Muslims. That is a tricky way of doing business."

Jama said the militants were "bent on nothing but destruction" and aimed to sow division between Muslims and non-Muslims.

"But that is something we need to fight," Jama said.

Kenyan police have arrested five suspects in connection with Thursday's attack at Garissa University College, not far from Kenya's border with Somalia, which left 147 people dead, Interior Minister Joseph Nkaissery said Friday.