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Several dozen people have been killed in a spasm of intercommunal violence in a disputed area on the-Sudan border, the UN's emergency response agency and a local official said on Wednesday.

OCHA said the fighting in the oil-rich Abyei area had left 36 people killed as of March 6, with an unknown number injured and reportedly 50,000 .

"Intercommunal tensions increased in recent weeks in the Abyei Administrative Area (AAA), allegedly driven by longstanding territorial disputes, inter-tribal tensions and revenge seeking," the agency said in a statement.

It said the fighting had been continuing since February 10 but intensified in early March, adding that humanitarian operations in the affected areas were suspended and relocated to safety.

Abyei has been contested since gained independence from Sudan in 2011, although there have long been tensions between the Ngok Dinka community and Misseriya herders who cross the area looking for grazing.

Abyei Administrative Area spokesman Ajak Deng said two deadly attacks at the weekend were carried out by Misseriya herders and members of the armed with heavy weapons.

He said six people were killed on Saturday and another 27 on Sunday, adding that the situation remained tense and people were still living in fear.

The US embassies in Juba and issued a joint statement voicing their "great concern" at the escalation of violence in the area.

"We call on all sides to cease reprisals and return to dialogue," they said.

Abyei has been under UN protection since South Sudan's independence, and the United Nations Interim Security Force for Abyei (UNISFA) deployed there also voiced its concern at the bloodshed.

"This has led to the loss of life and is causing untold humanitarian suffering on the people as well as reversing gains made towards achieving peaceful coexistence in Abyei," UNISFA said in a statement on Tuesday.