Artillery fire, airstrikes and gun battles rocked Sudan's capital Saturday, witnesses told AFP.
While fighting rages, relief efforts have stalled after more than two months of conflict between rival generals.
Houses in Khartoum shook from the fighting that continued unabated, residents said, with entire families sheltering in place, running low on vital supplies in the baking summer heat.
The United Nations says nearly 1.5 million people have fled the capital since violence erupted in mid-April, pitting the regular army against the paramilitary Rapid Support Forces.
Entire districts of Khartoum no longer have running water, and those who remain in the city have had no electricity since Thursday, several residents told AFP.
The battle for power between army chief Abdel-Fattah Burhan and his former deputy, RSF commander Mohamed Hamdan Dagalo, has killed more than 2,000 people, according to the Armed Conflict Location and Event Data Project.
Two-thirds of health facilities in the main battlegrounds remain out of service, according to the Sudanese doctors' union. The few hospitals still operating are extremely low on medical supplies and struggling to obtain fuel to power generators.
The U.N. says a record 25 million people, more than half of Sudan's population, are in need of aid and protection.
Aid has reached at least 2.8 million people, the U.N. said, but agencies report major hurdles to their work, from visas for foreign humanitarians to securing safe corridors.
"The army is ... loath to let aid into the capital, fearing that packages will end up in the RSF's hands" as has happened before, "allowing the paramilitary to hold out longer," according to think-tank the International Crisis Group (ICG).
The United States, which along with Saudi Arabia sought to mediate between the warring sides and ensure humanitarian aid can reach those in need, said Thursday it had put its efforts on hold.
"Both sides seek to use the humanitarian talks for tactical advantage ... with the military demanding that the RSF vacate residential areas and the RSF demanding that the army cease its aerial barrages," ICG said this week in a report.
Haven for mercenaries
No side appears willing to stand down, exacerbating the risk of prolonged conflict with regional ramifications.
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More than 150,000 people have fled Darfur over the border to Chad, according to the International Organization for Migration.
Chad, which already hosted more than 680,000 refugees, needs massive financial and technical support to confront this "unprecedented migratory crisis," Prime Minister Saleh Kebzabo said Saturday.
Dagalo's RSF have their origins in the Janjaweed militias that former strongman Omar al-Bashir unleashed in response to a rebellion by ethnic minorities in Darfur in 2003, drawing charges of genocide, war crimes and crimes against humanity.
"A collapsed Sudan could create a haven for transnational militants ... mercenaries and traffickers who could plague the country's neighborhood for years to come," ICG warned.
Maha Abdullah, 50, a tearful Sudanese woman who was able to reach Saudi Arabia for the hajj pilgrimage, sees only one solution: "It needs God's intervention to change things."