Sudan's warring military factions signed a commitment to respect humanitarian principles in their spiralling conflict late Thursday but they did not reach a ceasefire in talks described by US diplomats as difficult.

Nearly one month after the eruption of violence that has killed more than 750 people, injured 5,000 and displaced more than 900,000 others, the two sides promised in talks in the Saudi port city Jeddah to protect civilians, but nothing looked set to change immediately.

"We agree that the interests and well-being of the Sudanese people are our top priority and affirm our commitment to ensure that civilians are protected at all times," said envoys from army chief Abdel Fattah al-Burhan and paramilitary commander Mohamed Hamdan Daglo.

"This includes allowing safe passage for civilians to leave areas of active hostilities on a voluntary basis, in the direction they choose," the declaration said.

The agreement commits both sides in general terms to let in badly needed humanitarian assistance after looting and attacks targeting aid in the impoverished country, Africa's third largest in area.

The declaration calls for the restoration of electricity, water and other basic services, the withdrawal of security forces from hospitals and "respectful burial" of the dead.

The United States and Saudi Arabia, which are together leading the diplomatic drive, said that talks were ongoing with a proposal on the table for a 10-day truce, which would lead, in turn, to negotiations on a longer-term end to fighting.

But fighting and looting raged most of Thursday in the capital Khartoum and US diplomats were frank about the obstacles in the nearly week-long talks in Jeddah.

"This is not a ceasefire. This is an affirmation of their obligations under international humanitarian law," said a US official involved in the talks, who called the two sides "quite far apart".

"We are hopeful, cautiously, that their willingness to sign this document will create some momentum that will force them to create the space" to bring in relief supplies, she said.

At least 18 humanitarian workers have been killed since the war started on April 15, with many NGOs and United Nations agencies at least temporarily suspending work.

The UN's World Food Programme said millions of dollars worth of food was looted in Khartoum.

- Move to monitor future truce -

The conflict erupted when the paramilitary Rapid Support Forces -- set up and groomed by former dictator Omar al-Bashir for a scorched-earth campaign in Darfur -- refused to be integrated into Sudan's army under a planned transition to civilian rule.

The Forces of Freedom and Change, the pro-democracy force sidelined in a 2021 putsch by the two generals now at war, saluted the Jeddah declaration as "a first step in the right direction."

The UN-led support mission for Sudan, which also includes the African Union and regional IGAD bloc, also welcomed the declaration and called on the warring factions to "convey clear and unequivocal instructions to lower ranks" to allow humanitarian access.

After previous truces evaporated, the United States said the two sides also agreed in Jeddah for the first time on ways to monitor any ceasefire.

A second US official said the negotiations were "very tough" and acknowledged that both sides may have ulterior motives for ceasefire monitoring.

"Candidly, there is some hope on both sides that the other side would be seen as being the perpetrator of violations," he said.

"Frankly, we've seen violations by both sides in all the ceasefires to date and don't expect that to change."

But, he added that the length of time spent in brokering the first step would at least make the ceasefire more "effective" if reached.

Diplomats and experts have questioned whether the two sides want peace or if they are more interested in vanquishing the other.

Also Thursday, the United Nations' top rights body narrowly decided to beef up monitoring of abuses in Sudan, expanding the work of an existing special rapporteur.

But the vote was close. The move was led by Western countries, with 18 members of the Human Rights Council in favour, 15 opposed and 14 abstaining.