By Jonah Fisher
BBC News, Sudan
The United Nations says five of its staff have been assaulted by police in Sudan's Darfur region.
Aid workers have been in Darfur since conflict broke out in 2003
The UN workers were among 20 aid workers and African Union peacekeepers arrested by Sudanese authorities after a raid on a party at the weekend.
A statement from the UN said that some of their staff had suffered serious injuries and that it would protest officially to the Khartoum government.
UN workers are providing vital aid in the conflict-hit region.
The Sudanese government has not intervened to protect Darfur's battered population from the brutal Janjaweed militia. But when aid workers, African Union peacekeepers and UN staff held a Friday night party in Nyala - Darfur's biggest town - it felt it had to step in.
Sudanese police and security officers stormed the aid compound where the event was being held.
According to the UN, the 20 arrested people were physically and verbally assaulted with some seriously injured and needing medical treatment.
A report on Sudan's state-owned television said the UN and African Union workers had been detained for misconduct, comparing it to allegations of sexual abuse which face peacekeepers in southern Sudan.
A statement from the United Nations said all the detainees had now been released, but it also said it was deeply concerned about the treatment of its staff and that the basic principles of rule of law had been violated.
Northern Sudan is governed by Islamic Sharia law which outlaws the drinking of alcohol.
Its consumption by foreigners, within the privacy of their own homes, is usually tolerated.