"The alarming accounts of sexual violence that are heard from people who have fled to Port Sudan are just a fraction of those being repeated at a sickening scale from conflict hotspots across the country," said senior U.N. aid official Edem Wosornu.

War broke out on April 15 - four years after the overthrow of former President Omar al-Bashir during a popular uprising. Tensions between the army (SAF) and the paramilitary Rapid Support Forces (RSF), which jointly staged a coup in 2021, erupted over disagreements about a plan to transition to civilian rule.

"The fighting in Darfur continues to reopen the old wounds of ethnic tension of past conflicts in the region," Martha Ama Akyaa Pobee, a senior U.N. official on Africa, told the council. "This is deeply worrying, and could quickly engulf the country in a prolonged ethnic conflict with regional spillovers."

In the early 2000s "Janjaweed" militias - from which the RSF formed - helped the government crush a rebellion by mainly non-Arab groups in Darfur. Some 300,000 people were killed, the U.N. estimates, and Sudanese leaders are wanted by the International Criminal Court for genocide and crimes against humanity.

The current war has seen more than 4 million people flee their homes, of which 3.28 million are internally displaced and over 900,000 have crossed the borders into Chad, Egypt, South Sudan and other countries, according to the International Organization for Migration.

"The humanitarian impacts are made worse by credible evidence to suggest serious violations of international humanitarian law by both the SAF and the RSF which could amount to war crimes and crimes against humanity," Britain's U.N. Ambassador Barbara Woodward told the Security Council.

Russia's Deputy U.N. Ambassador Anna Evstigneeva said Moscow was concerned by the situation in Sudan and pledged support for the Sudanese authorities. She accused Western countries of interfering with the Sudanese internal political process and slammed the use of unilateral sanctions.

Both sides in the Sudan conflict have claimed military advances in recent days but there are no signs of a decisive breakthrough. Efforts by Saudi Arabia and the United States to secure a ceasefire have stalled.

U.S. Ambassador to the U.N. Linda Thomas-Greenfield told reporters after the council meeting that both sides were responsible for ethnic and sexual violence, adding: "There are no innocents here."

Sudan's U.N. Ambassador Al-Harith Idriss Al-Harith Mohamed told the Security Council that Sudanese troops "are not involved in any sexual or gender violence and the party involved in this atrocity is very well known."

In response to a request for comment, the RSF said allegations of rape by their forces were being promoted by supporters of Bashir's regime aligned with the army. The RSF would cooperate with any independent investigation into such allegations or into claims of violations against civilians in Darfur, the group's media office said.

(Reporting by Michelle Nichols; additional reporting by Aidan Lewis; Editing by Cynthia Osterman and Stephen Coates)

By Michelle Nichols