The US Air Force dropped such a bomb, officially designated as the GBU-43 Massive Ordnance Air Blast (MOAB) on suspected ISIS fighters in eastern Afghanistan last month. The nickname was widely used in briefings and reporting on the attack.
"I was ashamed when I heard the name," Pope Francis told an audience of students on Saturday. "A mother gives life and this one gives death, and we call this device a mother. What is happening?"
Pope Francis is set to meet US President Donald Trump on May 24 in a potentially awkward encounter given their opposing positions on immigration, refugees and climate change.
(Reporting by Agnieszka Flak; Editing by Angus MacSwan)