* Aid workers, rights group say more than 40 people killed
* The displaced people's situation could deteriorate - ICRC
* Government forces and rebels clashed in North Darfur
By Alaa Shahine
KHARTOUM, Oct 25 (Reuters) - Tribal fighting killed more than 40 people and displaced thousands of civilians, mostly women and children, in the state of South Darfur in Sudan this month, aid workers and a rights group said.
In North Darfur, rebels said on Saturday that government forces clashed with a faction of the Sudan Liberation Army (SLA) a day earlier. The Sudanese military could not confirm the incident but said it has forces operating in the area.
The fighting in South Darfur broke out early in October between the Arab Maaliya tribe and the African Zaghawa over cattle and other livestock around the town of Muhajiriya, an international aid source said on Saturday.
Analysts who follow Darfur say the Zaghawa tribe has settled in areas including Muhajiriya and demanded ownership of land, ignoring the rights of historical owners who include Maaliya.
"Fifty-one men from both sides were killed," the source told Reuters on Saturday, speaking on condition of anonymity. The U.S.-based Human Rights Watch said on Friday night more than 40 "civilians" were killed in the fighting.
The violence in Darfur threatens efforts to end the conflict which international experts estimate has claimed the lives of 200,000 people and forced 2.5 millions to flee their homes since 2003. Khartoum estimates the death toll at 10,000.
The International Committee of the Red Cross (ICRC) said it provided sleeping mats, clothes and tarpaulins last week to more than 4,000 people "displaced by communal clashes" around Muhajiriya.
"People were left without the bare necessities," said Juan Carlos Carrera, the head of the ICRC sub-delegation in Nyala, the capital of the South Darfur state.
The majority of the displaced sought shelter under trees and on a nearby seasonal river where water was readily available but their living conditions could "quickly deteriorate" with winter approaching, the ICRC statement added.
FREE-FOR-ALL
The conflict in Darfur that started in 2003 by mainly non-Arab rebels against the government has turned into a free-for-all crisis, with insurgents, bandits, government forces and tribes vying for everything from power to cattle and land.
Human Rights Watch said Khartoum-backed Arab militia attacked more than 13 villages between Oct. 5 and 17, burning homes and stealing livestock.
"Once again, civilians are bearing the brunt of fighting in Darfur," said Georgette Gagnon, Africa director at Human Rights Watch.
Officials from South Darfur Governor Ali Mahmoud's office were not immediately available to comment.
But a spokesman for the Sudanese military denied that government forces were involved, and said on Saturday that the fighting was between the Maaliya tribe and a faction of the Sudan Liberation Army (SLA) rebel group.
Two aid sources confirmed the fighting was tribal and that government troops were not present.
At the time of the fighting, a rebel leader said pro-government Arab militias ambushed fighters from an SLA faction and the United Resistance Front east of Muhajiriya.
In October 2007, at least 30 civilians were killed and 100 houses torched when militias with apparent army support attacked Muhajiriya, a U.N. report says. Khartoum denied any involvement.
The latest fighting in North Darfur erupted on Friday between the government and an SLA faction headed by Abdel-Wahed el-Nur, said Suleiman Jamous, a leader of the SLA/Unity faction. He said the clashes started "by accident" on a road near the area of Anabaji. He had no details of casualties.
Noureddine Mezni, spokesman for the United Nations/African Union peacekeeping force in Darfur, confirmed he had preliminary information of fighting in North Darfur but gave no details. (Writing by Alaa Shahine; editing by Sami Aboudi)