The United Nations says it is speeding up efforts to move refugees from a camp in South Sudan threatened by fighting along the border with Sudan.

The U.N. refugee agency said Friday the violence appears to be nearing the Yida refugee settlement.

Spokesman Melissa Fleming said the agency will move the camp's 20,000 refugees to safer locations further inside South Sudan. She said some refugees fearing attack have already fled into the bush.

Earlier this week, newly-independent South Sudan accused the north of invading its territory and occupying the town of Jau.

South Sudan claims Jau is located inside Unity state, while Sudan puts the town inside its own state of Southern Kordofan.

The U.N. agency says more than 50,000 refugees have fled into South Sudan in recent months to escape fighting in Southern Kordofan and neighboring Blue Nile state, where Sudanese forces are fighting rebels.

The fighting has raised concerns that Sudan and South Sudan are on the brink of war.

Tension between Sudan and South Sudan has run high since the south declared independence in July, after more than two decades of war.

The two countries have disputes over borders and oil revenue-sharing, and accuse each other of supporting rebels in the other's territory.