Escalating violence in Darfur, which has forced more than 80,000 people to flee their homes in the past six weeks and prompted several relief agencies to relocate staff, is jeopardising humanitarian operations in the western Sudanese region, aid workers said.

"The more violence there is in Darfur, the more difficult it is for the aid community - and even more so for the people who live there," Jessica Barry, spokesperson for the International Committee of the Red Cross (ICRC) in Sudan, said on Monday. "The general situation is such that people in villages are not able to live safely."

Violent attacks have recently spiralled across Darfur. On Saturday, an estimated 30 people were killed near Sirba, West Darfur State, when armed men riding on horseback attacked a commercial truck carrying civilians and relief items. "Some of the passengers were shot by the attackers and others were burnt to death during the attack," the United Nations Mission in Sudan (UNMIS) said on Sunday.

"The security situation in Darfur remains volatile," it added.

Last week, a compound used by the ICRC in North Darfur State was attacked, forcing the organisation to temporarily relocate 10 international staff from Kutum to El Fasher, together with a delegate from the Spanish Red Cross. "Unable to break the locks, the men fired several shots into the house, which was clearly marked as an ICRC building," it said in a statement on Friday. "[The] attack jeopardises vital humanitarian action."

Goal, an Irish NGO, also moved its staff out of the area. On 5 December, the UN and other international non-governmental organisations had withdrawn 124 non-essential staff from El Fasher to the capital of Khartoum, while about 200 remained to continue delivering humanitarian aid, UNMIS said.

The relocations were prompted by clashes between the Sudan Liberation Army (SLA) and Arab militias in El Fasher. According to the African Union Mission in Sudan (AMIS), armed Arab militia, known as Janjawid, stormed a market and opened fire, leading to a clash with SLA fighters. Five Arab militia, two SLA members and a civilian were reportedly killed.

"The situation in El Fasher, at the moment, is very worrying because there are many people in the town," Barry said. "Civilians need protection to be able to sustain their lives. It is why we are asking for security guarantees. At the moment it is a very complicated, very difficult situation," she added.

Violence has also affected operations in South Darfur State where three NGOs on Saturday temporarily relocated 30 staff members from Al Daien to Nyala due to tensions in the area. Other aid workers were relocated from Khor Abeche to Nyala after a group of armed men in uniform forced their way into their compound, manhandled staff at gun-point and took three vehicles and a phone.

"The security situation in Darfur remains volatile," UNMIS said. "As a result, more humanitarian workers have been relocated over the last three days from different areas in North and South Darfur."

Twelve humanitarian workers have been killed in Darfur since May.

In New York, the UN Secretary-General expressed alarm at the devastating impact of violence on Darfur's civilians. Of the more than 80,000 people newly displaced civilians, 50,000 are in Darfur and 30,000 in Chad. Several hundred civilians, including women, children and elderly, have been killed.

There were also very disturbing reports of mass rapes and other gross violations of human rights. The violence, a spokesman for the Secretary-General said on Thursday, could cut off almost one million people across Darfur from desperately needed humanitarian relief.

"Recent clashes between armed militia and SLA elements in El Fasher … are threatening relief operations for more than 1.3 million people across North Darfur," the Secretary-General's spokesman said. "The fighting has also interrupted UN support to AMIS," he added, noting that violence in Chad was disrupting relief operations to more than 300,000 people.

Security in North Darfur has deteriorated since the signing of the 5 May Darfur Peace Agreement (DPA) between the Sudanese government and an SLA group, led by Minni Minnawi. An African Union mission of 7,000 peacekeepers, whose mandate has been renewed for six months after Sudan rejected a proposal that would have beefed it up with 17,000 UN troops and 3,000 police officers, has not been able to contain the situation.

The violence, according to observers, has increased largely due to the fragmentation of rebel groups and fighting between the signatories and rebels that refused to sign the peace deal.

At least 200,000 people are estimated to have died since the Darfur conflict began in 2003 between government forces, allied militias and rebels seeking greater autonomy. More than two million people are displaced.

Meanwhile, thousands of women gathered in various world capitals and outside Sudanese embassies on Sunday to protest against the rape and sexual violence in Darfur. The Global Day of Action for Darfur called for the immediate deployment of an international peacekeeping force, with the mandate and capacity to effectively protect civilians.

"The situation in Darfur constitutes one of the most serious attacks on women’s rights anywhere in the world," Globe for Darfur, a coalition of dozens of organisations around the world, which coordinated the protests, said.