Pope Francis has condemned as "slave labor" the working conditions of victims of a factory collapse in Bangladesh last week that killed more than 400 people.

The Pope made the remarks in a private impromptu sermon at his personal morning Mass in his residence on Wednesday, which marked Labor day. He noted that the victims received 38 euros a month' for their hard work.

The pontiff also said that unjust salaries and the unbridled quest for profits go "against God."

These are the pope’s toughest words on workers’ rights since he took office in March.