"If ever there were an 'invisible' emergency, this is it," UN High Commissioner for Refugees (UNHCR) spokesman Ron Redmond said of the influx which saw 25,000 new arrivals this month alone.

The refugees, who are scattered along a 600-kilometre stretch of the remote and volatile border between Chad and Sudan, have received little international help. "Many are in poor health," Mr. Redmond told the press in Geneva, "making it all the more urgent that they be moved further inland."

Since April, 91,000 people have arrived, most of them living in makeshift camps along the Chad-Sudan frontier, where cross-border incursions are common.

Mr. Redmond said UNHCR was sending an eight-member emergency team to eastern Chad next week to prepare the transfer of thousands of refugees to Farachana, about 55 kilometres from the border. The site will need water wells and a basic road network before it can be ready for an initial group of 10,000 refugees in mid-January.

UNHCR is also looking at other possible sites for relocation. Meanwhile, it has distributed emergency aid to more than 10,000 vulnerable refugees along the border.

Some estimates place the number of internally displaced Sudanese in the Darfur region at over 600,000. This displacement is only the latest in 20 years of civil conflicts that have uprooted more than 4 million people inside Sudan, and driven another 570,000 into neighbouring countries.