Pope Francis has warned the rich and powerful that God will judge them on whether they fed the poor and cared for the Earth.

Francis' delivered the warning Tuesday during a Mass for the Vatican's Caritas Internationalis charity federation. It was his latest exhortation ahead of the release of his eagerly-awaited encyclical on the environment, which is expected sometime next month.

He said: "We must do what we can so that everyone has something to eat, but we must also remind the powerful of the Earth that God will call them to judgment one day, and there it will be revealed if they really tried to provide for him in every person and if they did what they could to preserve the environment so that it could produce this food."