Heavy fighting in Malakal in northeastern South Sudan killed dozens of people over the weekend, a military spokesman has said, after rebels reported they would try to seize control of the town.

At least 56 rebels and four government soldiers were killed with another 20 army officers injured, army spokesman Lul Ruai Koang said.

"Our forces were able to successfully drive them (rebels) back with heavy casualties. Over 56 rebels were killed," he told a group of journalists whom the government had flown to Malakal on Sunday to see the situation.

"We came here ... to let the people of South Sudan, and in particular the region, know that Malakal was not captured by the rebels as reported over the weekend."

It was not possible to independently verify the reported casualty figures, but a Reuters photographer who flew to Lalo, a camp near Malakal, with the military saw 15 bodies nearby, a burnt building within the base, and bodies scattered in other positions. Soldiers said they were expecting another attack.

On Friday, the rebels said they had captured Lalo and the nearby location of Wajwok, and planned to seize Malakal.

"We want to make sure that the government are dislodged from the town and we take control," deputy rebel spokesperson Dickson Gatluak told Reuters by phone from the Ethiopian capital, Addis Ababa.

Oil-rich South Sudan descended into civil war in December 2013 when a row between President Salva Kiir and his sacked deputy Riek Machar ended with fighting that often occurred along ethnic fault lines. Both sides have targeted civilians, human rights groups say.

The fighting initially ended with a peace deal signed in 2015, but violations have been frequent, and heavy fighting broke out again in July. Machar fled the country and is now in South Africa for medical treatment.

READ: Machar leaves Sudan for South Africa

Gatluak said the international community's failure to enforce the 2015 agreement was a major reason for renewed hostilities.

"We realised that there is not any political space, there is not any political settlement in (the capital) Juba. The international community and the IGAD itself have failed us ... they failed to keep that fragile peace agreement," he said, referring to the Intergovernmental Authority on Development, a political bloc of East African countries.

Last week, violence in South Sudan killed at least 60 people, the military said. The United Nations said it had reports of civilians being burned alive in buses.

READ: Scores feared dead in separate attacks in South Sudan

-Reuters