Updated

Officials working to stop violence in South Sudan say that a cease-fire signed last month appears not to be holding.

Negotiators for the two warring sides appeared to put a plug in some of the vicious violence by signing a cease-fire on Jan. 23. But the fighting has continued since then, and may even be ramping up.

U.N. Secretary-General Ban Ki-moon on Wednesday said he is deeply concerned about "ongoing fighting and skirmishes" in two states inside South Sudan.

An internal security report from an aid group forum in Juba, the capital of South Sudan, said new fighting has been reported outside of Malakal, the capital of Upper Nile, an oil-producing state. Aid groups are being advised that a rebel force appears to be closing in on the city.