(adds Bush comment) By Alaa Shahine KHARTOUM, Dec 8 (Reuters) - Sudanese President Omar Hassan al-Bashir dismissed criticism by the U.N. secretary-general on Friday, saying the world body was making unreasonable demands and turning a blind eye to the activities of Darfur rebels. U.N. Secretary-General Kofi Annan said on Thursday the Sudanese government might have to answer "individually and collectively" for failing to protect the people of the troubled western region from killings, rape and destruction. Annan has been trying without success to persuade Bashir to accept a "hybrid" U.N.-African Union peace force in Darfur, where tens of thousands of people have been killed and 2.5 million people driven from their homes since early 2003. U.S. President George W. Bush, after a meeting with South African President Thabo Mbeki at the White House, called the situation in Darfur "dire" and said countries needed to work with Sudan to "enable a peacekeeping force into that country to facilitate aid and save lives". Bashir has rejected the U.N. proposal of a hybrid force, just as he rejected previously the idea of a wholly U.N. force, saying colonial powers want to reassert control over Sudan. Bashir told a news conference in Khartoum earlier on Friday the rebel National Redemption Front (NRF) was responsible for the recent trouble in Darfur, which has worsened despite a partial peace agreement signed in Nigeria in May. "If there are any problems in Darfur, it is because of the activities of the National Redemption Front, which was formed after the Abuja agreement," Bashir said. The front brings together Darfur rebel groups which rejected the agreement, signed in the Nigerian capital, Abuja, by the government and only one major rebel faction. "This group is receiving huge support in terms of weapons, equipment and vehicles through the border and this has not been condemned (by the United Nations and others)," Bashir said, referring to the border between Darfur and neighbouring Chad. "How come we are prevented from standing against the Redemption Front and at the same time called upon to protect the citizens from them?" Bashir said. LARGE SCALE VIOLATIONS U.N. High Commissioner for Human Rights Louise Arbour said there was a "state of denial" about what was happening in Darfur which she hoped would end at a session of the U.N. Human Rights Council on Tuesday. "The truth is that there are extremely severe violations of human rights on a very large scale perpetrated in a climate of virtual total impunity," Arbour told Reuters in Geneva. A number of aid agencies evacuated staff from Kutum in northern Darfur on Friday after unidentified gunmen attacked a house used by the International Committee of the Red Cross, aid workers said. Earlier this week violence in the main Darfur town of El Fasher forced the United Nations to evacuate 134 of its own and other aid agencies' staff. Diplomats say Bashir feels in a relatively strong position in rejecting U.N. troops because the United Nations is unlikely to deploy a force in Darfur without the government's consent. The United States is sending its special envoy to Khartoum in another attempt to persuade the government. U.S. envoy Andrew Natsios will arrive in Sudan on Saturday and will visit Khartoum, Darfur and southern Sudan before travelling to Chad, which has seen Darfur violence spill across its borders, on Thursday, said a U.S. official, who spoke on condition he not be identified. "When we're talking about an AU-U.N. hybrid force, being able to work closely with Chad in terms of the deployment of those forces would be quite important, we believe," said U.S. State Department spokesman Sean McCormack. The African Union has about 7,000 troops in Darfur but its force is widely viewed as lacking the funds, manpower and equipment to maintain security. The conflict began when the rebels, mainly from non-Arab farming communities, took up arms to prise more power from the central government in Khartoum. The government responded by recruiting auxiliary militia forces from among mainly Arab nomadic communities. Some of the militias have attacked and displaced peaceful villagers. (Additional reporting by Richard Waddington in Geneva and Jeremy Pelofsky in Washington)