By Opheera McDoom

KHARTOUM, July 24 (Reuters) - Violence and insecurity in Darfur has forced 25,000 more people from their homes and is straining the capacity of camps swollen with refugees fleeing conflict in western Sudan, the U.N. said in a report on Tuesday.

"Aerial bombings by the military continued to be reported in North Darfur up to late June while clashes between the military and rebel factions continued to be reported ... in various locations," the United Nations said in a statement.

The report said in May and June a further 25,000 people fled their homes, bringing the number of camp residents in Darfur to 2.2 million.

The United Nations said there are more than 200,000 Darfuri refugees in neighbouring Chad and 140,000 Chadians displaced by the Darfur conflict, which has bled across the border.

"A very visible consequence of the increasing pace of displacement is the increasing population of IDP camps -- many of which can no longer absorb new arrivals," the report said.

The report said one aid agency was asked to leave Kutum in North Darfur and that the number of aid workers in Darfur had fallen to 12,300, down 2,400 from a year ago. Access to those affected fell to 68 percent from 78 percent last year.

"At the same time the caseload of conflict-affected populations has increased by more than half a million, to 4.2 million, it said.

The report was issued on the same day U.N. and African Union Darfur envoys issued invitations to rebel factions to meet in Tanzania and negotiate a unified position ahead of peace talks with the government.

In a joint statement U.N. Darfur envoy Jan Eliasson and his counterpart Salim Ahmed Salim said the Aug. 3-5 meeting in Arusha will focus on "ensuring a speedy, negotiated and sustainable settlement of the Darfur conflict, including the format and venue of and participation in the negotiations".

The envoys did not say which of the more than dozen rebel factions had been sent invitations, describing them only as "leading personalities of the non-signatory movements to the Darfur Peace Agreement".

Only one of three negotiating factions signed a peace deal in the Nigerian capital Abuja in May 2006. The rebels further factionalised following the deal. Under Libyan and Eritrean mediation the groups have been trying to unite.

In more than four years of rape, murder and looting, international experts say 200,000 people have died. Khartoum puts the death toll at 9,000, blaming Western media for exaggerating the conflict.

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