Rebels in Sudan's war-torn region of Darfur said Sunday that government forces backed by bomber aircraft are pursuing a week-old offensive.

The rebels said that aircraft are carrying out daily bombing raids as government troops seek to drive out guerrillas from the National Redemption Front from their strongholds north of Darfur's provincial capital El Fasher.

The government, which on Thursday rejected a U.N. Security Council resolution paving the way for the deployment of a 20,000-strong U.N. force in the troubled western region, about a week ago launched a major attack reportedly involving thousands of troops and janjaweed militias in the northern part of Darfur.

CountryWatch: Sudan

This area is controlled by rebels which did not sign a U.S.-brokered peace deal in May aimed at ending a three-year conflict that has killed more than 200,000 people and displaced 2.5 million.

Rebel commander Abubakar Hamid Elnur said by satellite telephone from northern Darfur said that there were many civilian casualties. "The government is still bombing with aircraft. It is very difficult for us to protect our civilians, especially from the air," he told The Associated Press. Many civilians have fled their villages for the hills and valleys, according to the rebels.

Elnur said that the government forces were concentrated in the area of Um-Sidir and that heavy fighting had been taking place in recent days between Um-Sidir and Kulkul, a base abandoned by the rebels at the start of the current Sudanese offensive, which lies some 32 miles north of El Fasher.

A government armed forces' spokesman denied any aerial bombing of villages in northern Darfur and described current army activities in the area as administrative operations.

"The allegation that the army used military aircraft and bombed the area is false and unfounded," said the spokesman, who spoke on condition of anonymity because he was not authorized to speak to the media.

"The rebels are interpreting in their own interest ordinary administrative operations the army is conducting in the area," he added.

A top African Union official in Khartoum overseeing the May peace deal, Sam Ibok, said Friday that more than 20 civilians had been killed and more than 1,000 displaced since major clashes started early in the week according to reports from the affected areas.

An ill-equipped African Union force of 7,000 troops has been unable to stop the humanitarian catastrophe in Darfur, where the peace deal signed by the government and one of the ethnic African rebel groups operating in the region has had little effect.

The African Union has called for the U.N. to take control of the peacekeeping force, whose formal mandate expires on Sept. 30.

But Sudan's President Omar Al-Bashir has maintained steadfast hostility to the presence of the U.N. force, instead offering to send 10,000 government troops to Darfur.

U.N. Secretary-General Kofi Annan on Thursday released a letter he had sent to Al-Bashir urging him to accept a U.N force in Darfur, saying only an impartial peacekeeping force could implement the May peace deal.

Annan also expressed alarm over the recent deployment of large numbers of Sudanese troops in Darfur.

Earlier this week, the U.N.'s top humanitarian official, Jan Egeland, warned "a man-made catastrophe of an unprecedented scale" loomed within weeks in Darfur unless the Security Council acted immediately.

Egeland said there could be hundreds of thousands of deaths if aid operations collapsed. The operations are already at grave risk because of rising attacks against aid workers and massive funding shortfalls.

The conflict in Darfur began in 2003 when ethnic African tribes revolted against the Arab-led Khartoum government. The government is accused of unleashing Arab militiamen known as janjaweed who have been blamed for widespread atrocities.

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