(Adds comment by NGO, paragraphs 8-9) By Patrick Worsnip UNITED NATIONS, Nov. 7 (Reuters) - Sudanese regional authorities in south Darfur have expelled the chief U.N. humanitarian official, accusing him of unspecified rule violations, the United Nations said on Wednesday. Wael al-Haj-Ibrahim headed the U.N. Office for the Coordination of Humanitarian Affairs in the town of Nyala, which was in charge of aid for up to 1 million displaced people in the war-ravaged state, officials said. That is nearly half of the total number of people independent experts say have been forced from their homes in Darfur as a whole by four and a half years of conflict between government forces, allied militias and rebel groups. "The United Nations is extremely concerned about the ramifications of this decision," said U.N. spokeswoman Marie Okabe, adding that the directive by the state governor did not oblige al-Haj-Ibrahim to leave Sudan. Okabe said the expulsion violated agreements signed between the United Nations and the Sudanese government to facilitate aid in Darfur. She said the chief U.N. humanitarian coordinator in Sudan, Ameerah Haq, was taking up the issue with authorities in Khartoum. U.N. officials said the state governor's directive accused al-Haj-Ibrahim, a Canadian of Palestinian descent, of violating "rules of humanitarian action," but did not specify how he had had done so. The Aegis Trust, a British-based group that campaigns against genocide, said al-Haj-Ibrahim had been forced out for "resisting a policy that amounts to further ethnic cleansing" of Darfur's African population. "With no security to allow them to return home and rebuild, forced removal of the (displaced people) from the camps gives their inhabitants no choice but to leave the region or die," said Aegis chief executive James Smith. Both U.N. aid officials and independent charities working in Darfur have complained of bureaucratic harassment by Sudanese authorities. A 26,000-strong U.N.-African Union peace-keeping force is meant to deploy in Darfur in coming months to protect civilians, but difficulties in putting it together and gaining necessary agreements from Khartoum threaten to delay it. (Editing by Alan Elsner;)