Francis told the Faithful Sunday that the nuns "gave their blood for the Church" and that they were not only victims of the attackers but also of "this indifference of globalization."
The nuns were among 16 people killed Friday by gunmen who stormed a retirement home run by a charity established by Mother Teresa.
One official said the attackers were "extremists" and blamed Daesh (known as ISIL) for the attack.
In recent months, Saudi-backed al-Qaeda and ISIL terrorists have stepped up attacks in Aden as part of Riyadh’s plan to undermine Houthi revolutionary forces.
On March 26, Saudi Arabia and some of its Arab allies began to launch deadly airstrikes against the Houthi Ansarullah movement in an attempt to restore power to the fugitive former President Abd Rabbuh Mansour Hadi, a close ally of Riyadh.
The death toll from the Saudi-led war so far has reached more than 8000 people. More than half of the total population of Yemen, some 14.4 million people, are also food insecure due to ongoing conflict and import restrictions, according to the Food and Agriculture Organization (FAO).