Attacks by rival factions of the Dinka ethnic group in an area claimed by both Sudan and South Sudan killed at least 32 people over the weekend, a local official said on Monday.

Deadly violence is common in the oil-rich Abyei region, where Twic Dinka from South Sudan’s neighbouring Warrap State are locked in a dispute with Ngok Dinka from Abyei over the location of an administrative boundary.

On Sunday morning, Twic Dinka armed youth, backed by a local militia, attacked several Ngok Dinka villages northeast of Agok town, Bulis Koch, the information minister for Abyei Administrative Area, told Reuters.

Men in South Sudan army uniforms, backed by Twic Dinka fighters, also attacked Ngok Dinka settlements, Koch said.

Spokespeople for South Sudan’s army did not immediately respond to Reuters’ request for comment.

In a statement the United Nations Interim Security Force for Abyei (UNISFA) condemned the attacks and said it had bolstered security in the area by intensifying patrols and engaging Abyei political leadership and traditional leaders to calm tensions.

The UNISFA force commander asked “all communities to refrain from violence and commit to ensuring sustainable peace in Abyei,” the statement said.

Abyei has been claimed by Sudan and South Sudan since the latter declared independence in 2011. Abyei had a special administrative status, governed by an administration comprising officials appointed by Juba and Khartoum.

South Sudan descended into civil war shortly after independence. The conflict pitted President Salva Kiir and his allies against Vice President Riek Machar.

A peace agreement signed three years ago is largely holding, but the transitional government has been slow to unify the various factions of the military.