MOGADISHU — Somalia's al Shabaab insurgents said they were behind a bus attack in northeast Kenya that killed 28 people on Saturday, saying it was in retaliation for raids on mosques in the port city of Mombasa.

"The Mujahideen successfully carried out an operation near Mandera early this morning, which resulted in the perishing of 28 crusaders, as a revenge for the crimes committed by the Kenyan crusaders against our Muslim brethren in Mombasa," Sheikh Ali Mohamud Rage, al Shabaab's spokesman, said in an emailed statement.