In the worst bloodshed in Kenya in nearly two decades, four al Shabaab gunmen went on a killing spree on Thursday, hunting down and executing students in a campus in Garissa, a northeastern town 200 km (120 miles) from the Somali border.
The raid has put Kenya on heightened alert and spooked Christian congregations, who were horrified by survivor testimonies recalling how the Islamist militants had sought out Christians to take hostage and kill, while sparing some Muslims.
In the message directed at the Kenyan public, the al Qaeda aligned group said the raid was retribution for Kenya's military presence in Somalia and mistreatment of Muslims within Kenya.
"No amount of precaution or safety measures will be able to guarantee your safety, thwart another attack or prevent another bloodbath from occurring in your cities," the group said in an emailed statement received by Reuters in the Somali capital.