CAIRO (AP) — Tribal clashes in Sudan’s troubled Darfur region have killed at least 15 people in recent days, forcing authorities to deploy more troops, the state-run news agency reported.

The violence came as thousands of displaced people protested against a decision by the U.N. Security Council to end the mandate of a U.N.-African Union peacekeeping force in Darfur and replace it with a smaller political mission.

The clashes over the weekend in the town of Gereida in South Darfur province pitted the Fallata tribe against the Arab Masalit. The unrest poses a challenge to authorities in the capital, Khartoum, who are trying to end the country's long-running rebellions as part of a fragile transition to democracy following last year's overthrow of President Omar al-Bashir.

Al-Bashir waged a scorched-earth campaign against rebels in Darfur in the early 2000s. Some 300,000 people were killed and 2.7 million were forcibly displaced. The International Criminal Court later charged al-Bashir and others with genocide and crimes against humanity.

The latest violence comes amid tensions between military and civilian authorities, who are sharing power in a transitional government. Civilian leaders are demanding greater control and oversight over the military's economic assets, built up over decades of internal conflicts.

The violence was linked to a dispute over a water source, Omar al-Malek, a local leader, was quoted as saying by the state-run SUNA news agency late Sunday. It said the Fallata retaliated after two of its tribesmen were slain, killing at least 13 members of the Masalit and wounding at least 34 others.

Mahdi Musa, the governor of South Darfur, said authorities have deployed troops to help detain those implicated in the fighting.

“The era of reconciliation conferences is over, and the era of enforcing the law has come,” he was quoted as saying by SUNA. He was referring to recent negotiations to settle the dispute.

The clashes came after the U.N. Security Council voted unanimously last week not to extend the mandate of the joint mission, known as UNAMID, when it runs out on Dec. 31.

The UNAMID force, established in 2007, was the first joint U.N.-AU peacekeeping operation. Its withdrawal is expected to be completed by June 30.

The decision by the Security Council led to renewed protests Saturday and Sunday by thousands of people across the Sudan’s western region. The protesters, mostly displaced women and children, want the peacekeepers to stay.

Adam Regal, a spokesman for a local organization that helps run refugee camps in Darfur, said the UNAMID exit would create a “security vacuum” in a region with several active militias.

In an interview with The Associated Press earlier this month, Jeremiah Mamabolo, the joint U.N.-African Union envoy for Darfur, said the transitional government in Khartoum needs to embark on the “huge task” of gaining the trust of the local people.