Hundreds of women and children are fleeing Sudan's disputed Abyei region, where fighting this week has killed at least 70 people.
Witnesses say the clashes involved Misseriya fighters who are allied with northern Sudan and Ngok Dinka tribesmen who back the south.
Violence has been escalating in Abyei as south Sudan prepares to secede from the north in July.
South Sudan voted overwhelmingly to split from the north in a January poll that northern leaders have said they will accept. However, the sides have yet to agree on the future of the oil-rich Abyei region, which sits on the north-south border.
A scheduled referendum on which part of Sudan Abyei would join failed to happen, because the north and south could not agree on who was eligible to vote.
The oil-rich Abyei region was a battleground during Sudan's 21-year north-south civil war.
South Sudan experienced separate violence this week in Jonglei state, where forces loyal to a renegade army leader, George Athor, battled with southern army soldiers. The army says at least 40 soldiers were killed in that fighting.