In a speech on Wednesday, al-Bashir criticised UN resolutions calling for a UN troop deployment in Darfur as a violation of Sudan's sovereignty and said they "provoke the conflict in Darfur, instead of finding a solution for it".
Saud al-Faisal, Saudi Arabia's foreign minister said on Thursday: "Sudan has now agreed for the UN to provide logistical support to help African forces.
"This is a breakthrough that never happened before and we hope it leads immediately to a solution to the humanitarian tragedy in Darfur as soon as possible."
"Clearly, Darfur needs help from the rest of the world"
Jack, Houston, USA
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After the talks, the Arab League said Ban and al-Bashir agreed on "practical measures" to implement a pact on peacekeeping in Darfur, made in Abuja, Nigeria, in November.
The sides agreed to "define the size of the African forces and their weaponry as well as the logistical and technical support, supervision, financing and the ways of participation by the United Nations".
But Washington, which calls the situation in Darfur genocide, was not impressed.
"We are very sceptical that Bashir has agreed to any such thing. We must see the fine print," a senior official told Reuters.
Before the Saudi announcement, US officials from the state, defence, treasury and other departments said Washington would "tighten the screws" with fresh sanctions within days.
Besides imposing travel and banking restrictions on at least three people, including a rebel leader, it wants to put more pressure on fragmented rebel groups.
About 130 firms linked to Sudan's government have been barred from doing business with the US or using US financial institutions.
Khartoum said on Thursday the new US measures would serve to threaten the agreement and fuel violence in Darfur.
Some say the fresh sanctions are too little, too late.
John Prendergast of the International Crisis Group said: "This is the right idea but it is simply not enough and not multilateral enough to make an impact, a dent, in the calculations of the Sudanese regime."
Experts say at least 200,000 people have been killed and 2.5 million displaced in Darfur since 2003, when rebel groups took up arms against the government accusing it of neglect.
Khartoum says only 9,000 people have died and denies the allegations of genocide.
The under-manned and under-equipped 7,000-strong African Union peacekeeping force in Darfur has also failed to stop the violence.
Sudan signed an agreement with the UN to boost humanitarian work in the region this week.