The Duchess of Edinburgh has described distressing scenes of sexual exploitation, after meeting refugees from Sudan's civil war who had fled to neighbouring Chad.

"People are having to exchange food and water for sex, for rape. That is violence that is being enacted through conflict. It is being used as a bargaining tool," said Sophie, after a visit to this conflict-hit region of Africa.

She spoke to women who had travelled into Chad to escape the conflict across the border in Sudan.

"These women have no option but to leave. And, even then, they're lucky if some of them can get away, because... if they leave their houses they get killed," said Sophie, who was moved to tears by the harrowing testimonies.

This was the first royal visit to Chad and the three-day trip, carried out at the request of the UK's Foreign Office, was not officially announced until it was over on Monday.

The purpose of the visit, says Buckingham Palace, was to draw attention to the deteriorating humanitarian crisis caused by the war in Sudan, which was now producing challenges for neighbouring Chad.

More than 10 million people have been forced to flee their homes by the conflict in Sudan, says the Palace, with women and children a high proportion of those now arriving as refugees in Chad.

"This is a human catastrophe that is vast and Chad is having to pick up the pieces when it can ill afford to do so," said Sophie.

At a medical centre in Adre, near the border with Sudan, Sophie told the Press Association about the "devastating" experiences that had been described to her and how it had upset her.

"What they do to the children is... I can't even use the words," she said.

Sophie had spoken to a woman who had fled from a town in the west Darfur region of Sudan, with the population facing threats and violence.

Her son and brothers had been rounded up and taken away and Sophie said the woman had seen bodies piled up in the street "like a wall".

The duchess, 59, had travelled to this part of Chad with Unicef representatives and visited a refugee camp where almost a quarter of a million people had gathered, with many more still arriving from Sudan.

She spoke to the mother of a small child who had travelled for 10 days to reach safety and did not know what had happened to her husband in the fighting.

"Whilst the world and its attention is being focused very much on other conflicts around the world, the humanitarian crisis being faced by the people of Sudan, which is landing on Chad's shores, cannot be ignored," said the Duchess of Edinburgh.

This is the latest visit by Sophie to highlight the issue of violence against women at times of armed conflict.

Earlier this year she became the first royal to visit Ukraine since the Russian invasion.

Her trips have often been to the type of destinations not usually on royal tours, including South Sudan, the Democratic Republic of the Congo, Iraq and Sierra Leone.