The United Nations refugee agency is expanding its operations in Darfur this year to protect more people in the war-torn Sudanese region, and appealed on Friday for $40.3 million to do so.

Some 2.5 million people have been uprooted during the five-year-old conflict which shows no signs of abating amid deteriorating security, the U.N. High Commissioner for Refugees (UNHCR) said.

"The challenges in Darfur have never been greater, with a pervasive conflict spreading across the region displacing more civilians and creating a very insecure environment for humanitarian workers," spokesman Ron Redmond told a briefing.

Preventing rapes and other sexual violence remains a priority, he said.

Some 260,000 Darfuri civilians fled fighting in 2007 alone, according to the Geneva-based UNHCR.

A major Sudanese government counter-offensive against rebel forces in West Darfur in February set off another round of displacement, it said. The U.N. has said 115 people were killed and 30,000 driven from their homes in the attacks on several villages using helicopter gunships and aircraft.

International experts estimate that some 200,000 have died in five years of violence which Washington calls genocide. Khartoum denies genocide and puts the death toll at 9,000.

Aid workers have increasingly become targets for robbery, car-jackings, and theft of equipment, the UNHCR said.

The appeal for 2008 doubles the amount sought last year for Darfur, where UNHCR also provides vital aid to 45,000 refugees from Chad and 2,500 refugees from the Central African Republic.

The agency, which now deploys 105 aid workers in Darfur, has mainly operated in West Darfur bordering Chad, but plans to extend operations to North and South Darfur, Redmond said.

In February it opened a field office in El Fasher, capital of North Darfur, where the U.N.-African Union (AU) peacekeeping mission in Darfur, known as UNAMID, is based.

Only 9,000 of the envisaged 26,000 UN-AU peacekeepers have been deployed in Darfur, a vast region roughly the size of France. Western governments have blamed Khartoum for the slow pace of deployment, saying it has dragged its feet in approving the force's composition and set up unnecessary obstacles.

Increasing the hybrid force to 26,000 has "faltered due to lack of air assets, troop contributions and bureaucratic process", the UNHCR said in an appeal document sent to donors.

"Five years since the armed conflict began, the major challenges remain physical insecurity, massive displacement and the occupation of land...," it said. "Comprehensive peace is unlikely to be established throughout Darfur in the short-term".