Several Sudanese policemen have been killed in a battle with rebels in Sudan's western Darfur region, the Sudanese government says.
Reports about the clash differ, with both sides claiming a crushing victory.
The government says its forces killed many rebels, while rebels from the Justice and Equality Movement (Jem) claim they killed about 50 police.
The joint UN-African Union peacekeeping mission in Darfur called on both sides to stop the fighting.
The battle started when Jem rebels attacked a government fuel and food supplies convoy in southern Darfur, the interior ministry in Khartoum said.
Police forces killed many of the rebels, the ministry added. It said several policemen had been killed, but gave no further details of casualties on the government side.
A Jem spokesman said his forces had killed about 50 men and "only a few" rebels had been injured.
The BBC's James Copnall in Khartoum says the clash is significant because it took place in southern Darfur, far away from what is usually recognised as Jem's stronghold in the north-west of the troubled region.
The fighting follows complaints from Sudanese and international human rights groups that more than a dozen Darfuri activists have been arrested in Khartoum in the last few days, our correspondent says.
Fighting intensified in Darfur in May after Jem walked out of peace talks with the government.
The Sudan Liberation Army (SLA) and Jem began attacking government targets in early 2003, accusing Khartoum of oppressing black Africans in favour of Arabs.
The conflict between rebels and government-backed militias is estimated by the UN to have cost the lives of 300,000 people and driven 2.7m people from their homes.
Sudan's President Omar al-Bashir denies committing war crimes in Darfur and says the number of those killed in the conflict is just 10,000.
A 22,000-strong joint United Nations and African Union peace force, known as Unamid, is on the ground in Darfur.