Pope Francis on Thursday denounced the murder of innocent women and children as the "horrid face" of war as he presided at a special prayer service for peace in South Sudan and the Democratic Republic of Congo.

Francis had planned to go later this year to South Sudan, which has been hit by civil war, famine and a refugee crisis, but had to scrap the project for security reasons.

During the service, which was punctuated by African singing in English, French, Italian and Swahili, Francis asked God to "break down the walls of hostility that today divide brothers and sisters, especially in South Sudan and the Democratic Republic of Congo."