The United Nations refugee agency says a rise in fighting in a once-peaceful part of South Sudan has forced tens of thousands of civilians to flee their homes since December.

Rocco Nuri, a spokesman for the agency, said Saturday that 23,000 civilians have fled their homes in South Sudan's Western Equatoria state, including 8,000 people who have left for neighboring countries.

Many are hiding in forests are beyond reach of aid groups, he added.

South Sudan's two-year conflict mostly focused in the country's northeast between government troops and rebel forces, but numerous militia have formed in Western Equatoria recently.

Rafael Patrick Zamoi, the governor of Western Equatoria, said the government aims to make peace with insurgents but will crack down on those causing instability.