Women and girls in Sudan's al-Obeid face a dire choice between the threat of drone attacks during the day and sexual violence at night when they go out to fetch water in the besieged city, UN Women said on Friday.

Access to food and healthcare is severely limited in al-Obeid, the capital of North Kordofan, where the UN's human rights chief warned this month that a human rights catastrophe was unfolding amid intensifying fighting between Sudan's army and the paramilitary Rapid Support Forces (RSF).

The war, now in its fourth year, has sparked one of the world's worst humanitarian crises - with rampant reports of sexual violence and other abuses.

"These women and girls have been harassed. They've been raped, and they've been subjected to other forms of sexual violence, all while trying to access water, one of life's most fundamental necessities in human rights," Anna Mutavati, UN Women Regional Director for East and Southern Africa, told reporters in Geneva via video link from Nairobi.

CRITICAL WATER SHORTAGES

UN High Commissioner for Human Rights Volker Turk said civilians in al-Obeid had faced siege-like conditions for 18 months, with critical ​shortages of clean water and relentless drone strikes - warning of a repeat of the atrocities that took place in al-Fashir in North Darfur last year.

There is no safe time for women and girls to collect water in al-Obeid, UN Women said, reporting that drone strikes on water sources by day have forced many to fetch water after dark, when they face harassment, rape and other sexual violence.

Across Sudan, an estimated 12.7-million women and girls are in need of support from gender-based violence services this year alone - a quadrupling since the beginning of the war, according to UN Women data.

The agency did not have a breakdown for al-Obeid, but highlighted that there were 500 000 people in the city, about 70% of whom are women and children, and said it expected high levels of need for support against sexual violence.

It said funding cuts to women-led organisations are shrinking the amount of support available, with two-thirds of women's organisations surveyed by UN women in Sudan reporting that safe spaces and gender-based violence services have either closed or been significantly reduced.