South Sudanese army captures key rebel base

South Sudan's army has captured the key rebel base of Nasir and the northern oil hub of Bentiu following a major offensive against opposition commander Riek Machar and his forces.

Army spokesman Philip Aguer told Al Jazeera the Sudan People's Liberation Army (SPLA) recaptured the towns of Nasir and Bentiu from Machar, who has been fighting government forces of President Salva Kiir since mid-December.

"The SPLA recaptured Bentiu and Nasir, Bentiu is now in the hands of the SPLA and government forces," said Aguer. "We are confident that the army is on the move to recapture all territories."

Nasir, near the border with Ethiopia, has been one of the main bases of Machar, the former vice president, and his army.

Government troops also moved into the northern oil hub of Bentiu, capital of the oil-rich Unity State and a town that has changed hands several times throughout the conflict.

Al Jazeera's Anna Cavell reporting from Juba said the capture of Bentiu represented a major victory for the government: "The capture of Bentiu will be celebrated by the SPLA, but we've seen the town change hands (five to six) times since the conflict first erupted."

Bentiu fell into rebel hands last month, and opposition forces were accused by the United Nations of the massacre of hundreds of civilians in the town.

Both sides in the conflict have been accused of war crimes including mass killings, rape, attacks on hospitals and places of worship, and recruiting child soldiers.

The advance by government forces comes just days after Kiir agreed to hold direct talks with Machar on ending the country's civil war during a visit by U.S. Secretary of State John Kerry.

Kerry had visited South Sudan on Friday and secured agreement from Kiir to meet with Machar in Addis Ababa in the coming days, with Ethiopian Prime Minister Hailemariam Desalegn acting as mediator.

However the independent Sudan Tribune website said it interviewed Machar in a rebel-held part of the country after Kerry's visit, and quoted Machar as saying that face-to-face talks "may be counter-productive."

President Barack Obama signed a decree last month authorizing punitive sanctions, including the seizure of assets and visa bans, against anyone in South Sudan deemed to be threatening peace efforts.

The conflict in the world's youngest country has claimed thousands of lives, with at least 1.2 million people forced to flee their homes.

Al Jazeera and wire services