An estimated 100 people have been killed in South Sudan in the latest of a series of ethnic clashes and cattle raids, officials say.Jonglei state Law Enforcement Minister Gabriel Duop Lam told the BBC that at least 200 people had been injured.The BBC's James Copnall, in Khartoum, says these figures suggest the attacks were on a very large scale.Cattle raids and revenge attacks have killed thousands of people in South Sudan since independence in 2011.Our reporter says the fighting involved rival groups from Jonglei state, who clashed over the border in Upper Nile state.Young men from the Murle ethnic group stormed several cattle camps on Friday, the local authorities said.Thousands of cattle are also reported to have been stolen in the raids, which targeted eight areas north of the town of Akobo.Jonglei state governor Kuol Manyang told the BBC that 100 people had been killed.In January, hundreds of Murle were killed in Jonglei by a force of about 6,000 fighters, mainly from the rival Lou Nuer ethnic group.Thousands of Murle fled their homes as a result of the attacks, which came in response to a massacre that left at least 600 people dead in August 2011.The Murle and the Lou Nuer have a long history of stealing each other's cattle, often prompting a spiral of violence.South Sudan's armed forces and the UN peacekeeping mission said they would send more troops to Jonglei state in response to those attacks.The latest violence comes as the authorities prepare to launch a disarmament campaign in Jonglei state.Some 12,000 soldiers and police are deploying to collect an estimated 30,000 weapons from Jonglei civilians.The UN says some 350,000 people were displaced because of intercommunal violence in South Sudan last year.South Sudan is one of the world's poorest regions and has hardly any roads, railways, schools or clinics as a result of two decades of conflict leading up to independence from Sudan in July 2011.