Pope Francis has issued his strongest condemnation yet of abortion, calling it a "horrific" symptom of a "throwaway culture" that places too little value on human life.

The pope, whom conservatives in the Roman Catholic Church have accused of not speaking out forcefully enough against abortion, made the remarks on Monday in his yearly 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. Pope Francis, in speech at 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, citing a "throwaway culture" that had enveloped many parts of 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 pope said.

Since his election in March, the pope has shown no signs of changing the church's anti-abortion position, but he has not spoken out against the practice as sternly or as repeatedly as his predecessors, Pope Benedict XVI and the late Pope John Paul II.

Conservatives in the Church were alarmed when Pope Francis, in a landmark interview in September with the Italian Jesuit magazine Civilta Cattolica, said the church must shake off an "obsession" with teachings on abortion, contraception and homosexuality.

His stance favouring mercy over condemnation has disoriented conservative Catholics and sparked criticism from highly placed members of the church.

In his wide-ranging speech at the Vatican on Monday, the pope also condemned the ongoing violence in Syria and other flashpoints around the world, saying peace was threatened by "every denial of human dignity".

In the part of his speech about children, Pope Francis also deplored their use as "soldiers, abused and killed in armed

conflicts; and children being bought and sold in that terrible form of modern slavery which is human trafficking."