Sudanese refugees flow into South Sudan's Upper Nile StateListen /
Thousands of refugees from Sudan have massed at a border area in South Sudan's Upper Nile State, according to the United Nations refugee agency (UNHCR).
UNHCR has warned of what it calls "a sharply worsening humanitarian situation" in that area.
The agency is also concerned about the safety of the refugees who are close to the border as fighting continues between Sudanese forces and rebels in Sudan.
To find out more about this, Derrick Mbatha spoke with Terry Ongaro of UNHCR on the line from Juba, the capital of South Sudan.