Pope Francis has criticized the naming of US military's biggest non-nuclear bomb as "The Mother of All Bombs", saying the word "mother" should not be used in reference to a deadly weapon.

The U.S. Air Force dropped such a bomb, officially designated as the GBU-43 Massive Ordnance Air Blast (MOAB) on suspected Islamic State 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.

Pope Francis, who's set to meet President Donald Trump on May 24, said,"A mother gives life and this one gives death, and we call this device a mother. What is happening?"