Updated

The United Nations says youth from South Sudan's second-largest ethnic group have forced their way into a U.N. peacekeeping mission base in conflict-wracked Jonglei state, pursuing of civilians who had taken refuge there.

U.N. deputy spokesman Farhan Haq said Thursday the U.N. fears "there may have been some fatalities but can't confirm who and how many at this stage."

Rapidly escalating ethnic violence has raised fears of instability in the world's newest country.

Haq says the situation in the capital, Juba, appears to have calmed to some extent, but he noted unconfirmed reports of several students killed by security personal at Juba University on Wednesday.

He says thousands have sought refuge and called for U.N. protection.