He said it was was “frightful” to think about early pregnancy terminations.
Since his election in March, the pope has not spoken out against abortion as sternly as his predecessors.
He made the comments is his yearly “State of the World” address to diplomats accredited to the Vatican.
“It is horrific even to think that there are children, victims of abortion, who will never see the light of day,” he said in part of the speech that addressed the rights of children around the world.
“Unfortunately, what is thrown away is not only food and dispensable objects, but often human beings themselves, who are discarded as unnecessary.”
The BBC’s Alan Johnston in Rome says that there has been concern in some quarters of Roman Catholicism that the pope has not been putting the church’s view on abortion forcefully enough.
Correspondent says that the Pope’s stance favouring mercy over condemnation has made more conservative Roman Catholics uneasy, but they will welcome his latest remarks.
Some months ago Pope Francis acknowledged that he had said little on issues like abortion and contraception.
But he explained that he felt it was not necessary to talk about these controversial questions “all the time”.