NYALA, Sudan (Reuters) -- Refugees released on Tuesday the last of the aid workers they had taken hostage in Darfur's largest camp, but police continued to detain one of their leaders, a U.N. spokesman said.Armed police had arrested a tribal leader on Sunday in Kalma camp outside Nyala in South Darfur state, prompting the camp residents to take up to 34 hostages to barter for his release, sources in the aid community said.The hostages were released gradually, with the last five, who worked in the government water and sanitation agency, freed on Tuesday evening, the sources said."Everybody has been released," said a U.N. spokesman from Khartoum. "But the sheikh is still being detained by the authorities."Kalma, which houses almost 90,000 Darfuris who have fled their homes during a 2 1/2-year-old revolt, has been a hotbed of unrest. Authorities have said rebels have launched attacks from within the camp.Camp residents have attacked and burned down the government humanitarian agency's offices in Kalma, complaining the officials did nothing to stop daily attacks and rape in and around the camp.The abducted aid workers were from the Sudanese Red Crescent, the U.S. CHF aid agency and the Sudanese water and sanitation agency (WES).The United Nations says at least 2 million Sudanese have been turned into refugees in their own country by fierce fighting between rebels, the Sudanese army and Arab militias known as Janjaweed, believed to be backed by Khartoum.U.N. officials say recent violence has hindered vital aid to the refugees and restricted the movement for many of the 11,000 humanitarian workers in the remote western region.Rape, murder and robbery are rampant throughout the vast region the size of France.Non-Arab rebels took up arms in early 2003, accusing Khartoum of neglect and of monopolizing wealth and power.The United States has called the violence genocide and blamed the government and its allied militias. Khartoum denies the charge but the International Criminal Court (ICC) is investigating alleged war crimes committed during the revolt.Copyright 2005 Reuters. All rights reserved.This material may not be published, broadcast, rewritten, or redistributed.