Pope Francis condemned on Friday an assault by Somali militants on a Kenyan university that killed at least 147 people, calling it an act of "senseless brutality".

Masked al Shabaab gunmen stormed the Garissa University College campus on Thursday and initially killed indiscriminately before freeing some Muslims and targeting Christian students.

"In union with all people of good will throughout the world, His Holiness condemns this act of senseless brutality and prays for a change of heart among its perpetrators," Vatican Secretary of State Cardinal Pietro Parolin said in a statement.

Parolin said the pontiff called upon "all those in authority to redouble their efforts to work with all men and women in Kenya to bring an end to such violence".

Francis has expressed alarm over the plight of Christians targeted for their faith, particularly by Islamic State in the Middle East, and has said the international community would be justified in using military force as a last resort to stop "unjust aggression".