Darfur has been riven by various armed factions
An upsurge in fighting in the Sudanese region of Darfur recently has displaced thousands more civilians, say aid agencies and human rights groups.
Human Rights Watch said that more than 40 civilians had been killed in attacks by pro-government Arab militias on rebel-held villages in South Darfur.
The International Committee of the Red Cross (ICRC) said thousands had fled the fighting in the last month.
It said that many were sheltering under trees and lacked basic supplies.
Up to 300,000 people have been killed and more than two million have fled their homes in Darfur since the conflict began in 2003.
Aid agencies say the latest violence happened in the area of Muhajiriya, east of the South Darfur capital, Nyala.
Human Rights Watch, quoting unnamed local sources, said that government-backed Arab militias attacked more than 13 settlements around Muhajiriya, burning homes and stealing livestock in operations against rebel forces.
"Once again, civilians are bearing the brunt of fighting in Darfur," said Georgette Gagnon, Africa director at the agency.
An aid worker in the area said that about 12,000 people had been displaced by the fighting, the AFP news agency reported.
The ICRC said that last week it provided sleeping mats, clothes and tarpaulins to more than 4,000 people, mostly women and children, displaced by "communal clashes" around Muhajiriya.
"People were left without the bare necessities," said Juan Carlos Carrera, head of the ICRC sub-delegation in Nyala.
There have also been reports of fighting in North Darfur.
Government forces clashed with a faction of the rebel Sudan Liberation Army (SLA) on Friday, a rebel spokesman said.
Suleiman Jamous, a leader of the SLA/Unity faction, said that clashes had taken place on a road near the area of Anabaji. He had no details of casualties.
The Sudanese military could not confirm the incident but said it has forces operating in the area.
Sudanese President Omar al-Bashir launched a new peace initiative for Darfur on 16 October, at a ceremony attended by regional dignitaries.
However, the rebels and opposition parties did not take part.
Judges at the International Criminal Court have asked for more evidence before deciding whether to issue an arrest warrant for President Bashir over war crimes allegedly committed in Darfur.
President Bashir denies the charges and Sudan has been lobbying to get the investigation delayed.