South Sudanese rebels defended their renewed offensive yesterday as condemnation grew of the massacre at the United Nations compound in Bor where women and children were attacked.

James Gadet Dak, spokesman for the rebel leadership, said militias had targeted oil-producing regions to stop the government of President Salva Kiir from using the revenue to engage Ugandan troops and Sudanese militias.

He insisted that the fighting was necessary to “put pressure on Salva Kiir”. If this did not force him to the negotiation table, he warned, then “we are coming to [South Sudan’s capital] Juba to depose him”.

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Thousands have been killed in South Sudan since tribal fighting began in December between supporters of MR Kiir and his former deputy, Riek Machar. More than one million people have fled their homes.

However, the sudden collapse last week of the ceasefire signed on 23 January has renewed chaos and raised questions about the viability of the state.

The UN Security Council met to address the attack on the base in Bor, which left at least 48 dead after a mob rampaged through the site. It warned that the action could “constitute a war crime”. The US embassy in South Sudan’s capital released a joint declaration with the European Union condemning “these atrocities in the strongest terms”.

Rebel groups targeted Bentiu, capital of the oil-producing Unity state, in the renewed offensive. Once in control, they ordered all oil firms operating in South Sudan, including India’s ONGC Videsh and the China National Petroleum Corp, to leave.

Government spokesman Ateny Wek Ateny said yesterday that fighting continued in the city as the army sought to regain control. However, poor communications made it difficult to establish the veracity of his claim.

The UN said it had been denied access to civilians, with rebel groups understood to be blocking the way.

“There has been direct targeted killing of people based on nothing else except their identity,” the local UN humanitarian co-ordinator, Toby Lanzer, said. “It is imperative that the United Nations and non-governmental organisations reinforce their ability in Bentiu.”