South Sudan's army battled rebels in the oil town of Bentiu Monday, damaging hopes of new peace talks to end a nearly five-month civil war.

Army spokesman Philip Aguer said there was heavy fighting Monday in the northern town but that government troops had the "upper hand."

Bentiu fell into rebel hands last month. The United Nations has accused the rebels of killing hundreds of people in the town, based on their nationality or ethnic origin. The rebels have denied carrying out the killings.

The fighting comes just days after U.S. Secretary of State John Kerry visited Juba in an effort to advance stalled peace negotiations taking place in Ethiopia.

During his visit, South Sudanese President Salva Kiir agreed to hold direct talks with rebel chief Riek Machar, but no date for the meeting has been set.

Months of political and ethnic violence across South Sudan have caused thousands of deaths and driven more than 1.1 million people from their homes. Tens of thousands are sheltering in U.N. bases throughout the country.

The United Nations has warned the country faces a possible famine unless farmers can quickly return home and plant their fields.