At least 139 people have been killed and 5,000 cattle seized in southern Sudan in clashes between rival tribes.
Reports indicate that Nuer tribesmen attacked Dinka cattle herders, who suffered most of the casualties.
Authorities in Juba, in southern Sudan, said Thursday they just learned of the tribal raids, which began in a remote area, Tonj, at the end of last week. U.N. aid officials are sending in a team to assess the situation.
Meanwhile, a coalition of aid groups warned Thursday that Sudan could return to civil war soon if there is no effective action by the international community to salvage the 2005 peace deal that ended 21 years of conflict.
The aid groups' report said violence in southern Sudan killed 2,500 people last year and forced 350,000 others to flee their homes. The report said the numbers eclipsed those recorded in Darfur during 2009.
Oxfam's Maya Mailer says it is "not yet too late," but the trend of increasing violence could make southern Sudan "one of the biggest emergencies in Africa in 2010."
Ten aid groups including Oxfam and Save the Children joined in the report. They noted this is a critical year for Sudan, which is to have the country's first multiparty elections in decades. Another potential "flashpoint," the report says, is an upcoming referendum on independence for the south.
The aid groups called on the United Nations peacekeeping mission to prioritize protecting civilians in Sudan. They also urged the international community to help mediate between the north and south ahead of the elections and referendum.
The 2005 Comprehensive Peace Agreement helped end Sudan's north-south civil war. The 21-year conflict is estimated to have killed around two million people.