VATICAN CITY, March 13 — Pope Francis issued his toughest condemnation yet of the invasion of Ukraine, saying today the "unacceptable armed aggression” must stop.

Speaking to thousands of people in St. Peter’s Square for his Sunday blessing, Francis also said that the killing of children and unarmed civilians was "barbaric” and with "no valid strategic reason”.

He called the besieged city of Mariupol a "martyred city” and again appealed for "truly secure humanitarian corridors” to allow residents to evacuate.

"In the name of God I ask you: stop this massacre!,” the pope said, adding that Ukrainian cities risked "being reduced to cemeteries”.

The pope has not used the word "Russia” in his condemnations of the war since Russian President Vladimir Putin ordered the invasion on Feb. 24.

But his choice of words, such as "armed aggression” and "no valid strategic reason,” appear aimed at contesting Moscow’s justifications for the invasion.

Russia calls its action a "special military operation”. Last Sunday Francis implicitly rejected that term, saying it could not be considered "just a military operation” but a war that had unleashed "rivers of blood and tears”.

Moscow says its action is designed not to occupy territory but to demilitarise and "de-Nazify” its neighbour. It has also denied targeting civilian areas. — Reuters